Enabling hardware switches to perform logical routing functionalities

ABSTRACT

A managed hardware forwarding element (MHFE) that performs packet forwarding operations for a logical network is described. The MHFE receives configuration data for the logical network that defines a logical router and a set of logical switches for logically connecting several end machines that operate on different host machines to several physical machines that are connected to the MHFE. The logical router also includes multiple routing components. The MHFE also receives a first forwarding table and a second forwarding table. The first forwarding table stores linking data for each logical port of each logical switch in the set of logical switches that identifies a corresponding routing component in the logical router. The second forwarding table stores a set of routes for each routing component of the logical router. The MHFE uses the first and second forwarding tables to perform packet forwarding operations at the MHFE.

BACKGROUND

There is a growing movement, driven by both industry and academia,towards a new network control paradigm called Software-DefinedNetworking (SDN). In Software-Defined Networking (SDN), a control planeimplements and maintains the control logic that governs the forwardingbehavior of shared network switching elements on a per user basis. Avirtual network that is implemented for a tenant of a hosting system isa good example of an SDN. The virtual (logical) network of a tenant ofthe hosting system connects a set of data compute nodes (e.g., virtualmachines) that are assigned to the tenant, to each other and to othervirtual and/or physical networks through a set of logical switches andlogical routers.

One of the challenges in today's hosting system networks is extendingthe virtual networks (e.g., of one or more tenants) to other physicalnetworks through hardware switches (e.g., third-party hardwareswitches).

BRIEF SUMMARY

Some embodiments provide a novel method of configuring a logical routerof a logical network on a managed hardware forwarding element (MHFE) inorder for the MHFE to implement the logical network and to performlogical routing functionalities. In some embodiments, the method isperformed by a control plane that configures and manages one or morelogical networks for one or more tenants of a hosting system (e.g., adatacenter). In some embodiments, a logical network of the hostingsystem includes a set of logical forwarding elements (e.g., logicalswitches and routers) that logically connects different end machines(e.g., virtual machines, containers, etc.) that run on different hostmachines. Some embodiments configure a logical router of a logicalnetwork on the MHFE (e.g., a third-party hardware switch such as atop-of-rack or TOR switch or other appliances such as firewalls, loadbalancers, etc.) to enable the physical workloads connected to the MHFE(e.g., third-party servers connected to a TOR switch) to exchangenetwork data with other end machines and/or external networks that areconnected to the logical network.

In some embodiments, the control plane receives a definition of alogical router (e.g., through an application programming interface orAPI) and defines several routing components for the logical router. Eachof these routing components is separately assigned a set of routes and aset of logical interfaces. Each logical interface (also referred to aslogical port) of each routing component is also assigned a network layer(e.g., Internet Protocol or IP) address and a data link layer (e.g.,media access control or MAC) address. In some embodiments, the severalrouting components defined for a logical router include a singledistributed router (also referred to as distributed routing component)and several different service routers (also referred to as servicerouting components). In addition, the control plane of some embodimentsdefines a transit logical switch (TLS) for handling communicationsbetween the components internal to the logical router (i.e., between thedistributed router and the service routers).

The control plane of some embodiments configures and manages one or morelogical networks for one or more tenants of a hosting system (e.g., adatacenter). In some embodiments, a logical network of the hostingsystem logically connects a set of end machines (e.g., virtual machines,physical servers, containers, etc.) and a set of physical machines usinga set of logical forwarding elements (e.g., logical L2 and L3 switches).In some embodiments, different subsets of end machines reside ondifferent host machines that execute managed forwarding elements (MFEs).The MFEs implement the logical forwarding elements of the logicalnetwork to which the local end machines are logically connected.Additionally, the logical forwarding elements are implemented by one ormore MHFEs in order to connect the physical machines that are connectedto the MHFEs to the other end machines of the logical network. In otherwords, each of the host machines executes an MFE that processes packetssent to and received from the end machines residing on the host machine,and exchanges these packets with other MFEs operating on other hostmachines as well as the MHFEs (e.g., through tunnels). The MFE of someembodiments is a software instance that is implemented in thevirtualization software (e.g., a hypervisor) of the host machine.

Some embodiments implement the distributed routing component of thelogical router in a distributed manner across the different MFEs and theMHFE. Some embodiments implement each of the service routing componentsof the logical network on an edge node (e.g., a gateway), which is amachine at the edge of the network (e.g., the datacenter network), inorder to communicate with one or more external networks. Each of theservice components has an uplink interface (port) for communicating withan external network as well as a TLS interface (port) for connecting tothe transit logical switch and communicating the network data with thedistributed routing component of the logical router that is alsoconnected to the transit logical router.

Some embodiments configure both the distributed component and theservice components of the logical router on an MHFE. In other words, insome embodiments, the MHFE acts as the edge node of the logical routerby implementing the service routers (components) of the logical routerfor exchanging network data with the external networks. When the controlplane receives a definition of a logical router, in which, the uplinkport of the logical router is bound to a physical port of an MHFE (i.e.,the physical port is assigned the same IP and MAC addresses of theuplink port), the control plane instantiates both the distributedcomponent and service components of the logical router on the MHFE. Thecontrol plane further defines a new uplink logical switch (ULS) forhandling the communications between the SRs implemented on the MHFE andthe external networks.

In some embodiments, the control plane defines the southbound interfaceof the uplink logical switch (ULS) to be associated with the physicalport of the edge MHFE that is assigned the MAC and IP addresses of theuplink port of the logical router. In some such embodiments, the controlplane defines the northbound interface of the ULS to be associated withan external network (e.g., a southbound port of a next hop physicalrouter that connects the logical network to one or more externalnetworks).

In order to configure and manage the different components of a logicalrouter as well as other logical forwarding elements (e.g., logical L2switches) of a logical network, some embodiments configure a set ofdatabase tables (e.g., forwarding tables of the forwarding elements) onthe MHFE using an open source protocol (e.g., an open vSwitch databasemanagement (OVSDB) protocol), which is recognizable by the MHFE. Such anopen source protocol requires minimal software to execute on the MHFE(e.g., TOR switch) and to enable the MHFE to implement the logicalnetwork forwarding elements (e.g., logical L2 and L3 forwardingelements) in order to communicate with the other machines connected tothe logical network as well as other external networks.

After generating the database tables on the MHFE using the open sourceprotocol (e.g., OVSDB), some embodiments use the database schema topropagate a particular one of the tables with the physical locatorinformation of the logical ports of the different routing components(i.e., distributed and service routers) of the logical router. Thephysical locator information, in some embodiments, specifies the tunnel(e.g., Virtual Extensible LAN (VXLAN) tunnel) endpoint addresses (i.e.,IP addresses) of the MFEs and MHFEs that implement the different logicalforwarding elements (e.g., logical L2 and L3 switches). This table (thetunnel endpoint locator table), in some embodiments, specifies thenetwork layer (IP) addresses of the MFEs and MHFEs that implement thelogical ports of logical switches to which the machines (e.g., endmachines, physical machines, etc.) and/or logical ports of the logicalrouters are connected. By locating the endpoints, the MFEs and MHFEs areable to establish tunnels between themselves and exchange the networkdata through the established tunnels (VXLAN tunnels).

In some embodiments, the generated tunnel endpoint locator table hasseveral fields including (i) a logical switch field that species thelogical switch to which a port of a machine or logical router isconnected, (ii) a MAC address field that specifies the corresponding MACaddress of the port, and (iii) a locator field that specifies the IPaddress of the tunnel endpoint for the corresponding MAC address. Inorder to configure the locator data of the logical ports of thedifferent routing components on the table, some embodiments populate arecord for each logical port of the distributed routing component in thetable in a first manner a record for each logical port of the servicerouting component in a second different manner.

For each port of the distributed component that is connected to alogical forwarding element (e.g., an L2 logical switch), someembodiments generate a record and stores (i) in the logical switchfield, the logical switch to which the port is connected, (ii) in theMAC address field, the MAC address of the port, and (iii) in the locatorfield, a fixed IP address of 127.0.0.1, or the localhost. The localhostis a loopback interface address (127.0.0.1) in networking which can beused to access the machine's own network services. In other words, whenthe MHFE (e.g., the VXLAN tunnel endpoint (VTEP) of the MHFE) realizesthat the destination MAC address of a packet belongs to a port of thedistributed routing component, the VTEP does not establish a tunnel forrouting the packet. This is because the distributed routing component isimplemented by every single MFE, MHFE, and gateway that participates inthe logical network. As such, a packet with a destination MAC address ofthe logical router is not required to be routed to any other node in thenetwork.

Some embodiments, on the other hand, populate the tunnel endpointlocator table with the tunnel endpoint data of each logical port of theservice routing components that is connected to a logical forwardingelement (e.g., an L2 logical switch). That is, for each logical port ofthe service routers, some embodiment store (i) in the logical switchfield, the logical switch to which the port is connected (e.g., thetransit logical switch to which the southbound port of the servicecomponent is connected), (ii) in the MAC address field, the MAC addressof the port, and (iii) in the locator field, the IP address of thetunnel endpoint that implements the logical switch port to which theservice component port is connected (e.g., the IP address of the gatewaymachine that implements the service routing component).

Some embodiments enable an MHFE (e.g., the hardware VTEP of the MHFE) toperform L3 routing functionalities on the packets that are destined forthe logical router implemented by the MHFE. In order for the hardwareVTEP to realize that a packet is destined for the logical router, thehardware VTEP must be able to identify the destination MAC address ofthe packet as a MAC address that belongs to a logical port of a routingcomponent of the logical router. In order to enable the hardware VTEP tomake such a determination, some embodiments use the database schema(e.g., OVSDB schema) to propagate configuration data that links thedifferent database tables generated on the MHFE.

Linking the different tables allows the hardware VTEP to search the MACaddress of the received packet against a logical router table that hasall the MAC addresses of the different ports of the different routingconstructs of the logical router. In OVSDB schema, among the differenttables (e.g., forwarding tables) that are generated and configured onthe MHFE, the control plane generates a logical router table on the MHFEthat maps the IP addresses of the different ports of the distributed andservice routing components of the logical router to the logical switcheswith which they are associated. On the other hand the tunnel endpointlocator table described above, includes the MAC addresses of all thedifferent logical ports of the routing components of the logical router.In order to link these two tables together, some embodiments store theIP addresses of the ports of the logical router in an optional field ofthe tunnel endpoint locater table while configuring this table. In otherwords, the control plane uses a field of the table that has optionaldata (i.e., the field may or may not be used) to propagate the linkingconfiguration data in the field.

By doing so, in some embodiments, the control plane is able to tag theMAC addresses of the logical ports of the logical router during theconfiguration of the tunnel endpoint locator table. That is, while thecontrol plane is configuring the tunnel endpoint locator table, thecontrol plane looks up the corresponding IP address of each port's MACaddress in the logical router table, and when a match found, the controlplane tags the corresponding MAC address of the port, in the tunnelendpoint locator table, as a logical router port's MAC address. As such,when a hardware VTEP receives a packet, the hardware VTEP simply looksup the destination MAC address of the packet in the tunnel endpointlocator table, and if the MAC address in the table is tagged as alogical router port MAC address, the hardware VTEP realized that thepacket is an L3 packet and starts L3 processing on the packet.

In some other embodiments, the control plane, although populates thelinking IP address in the tunnel endpoint locator table, does not tagthe MAC addresses during the configuration of this table. In some suchembodiments the hardware VTEP retrieves a corresponding IP address ofthe destination MAC address of the packet from the tunnel locator tableand matches the corresponding IP address against the IP addresses of allthe logical ports of the routing components that are stored in thelogical router table in the OVSDB schema (i.e., the logical router tableconfigured on the MHFE). When the hardware VTEP finds a match for the IPaddress in the logical router table, the hardware VTEP realizes that thedestination MAC address of the packet is in fact a MAC address of one ofthe logical router ports. As such, the hardware VTEP starts to performrouting functionalities on the packet (e.g., the hardware VTEP modifiesthe source and destination MAC addresses in the packet headers to routethe packet to the next hop).

The preceding Summary is intended to serve as a brief introduction tosome embodiments of the invention. It is not meant to be an introductionor overview of all of the inventive subject matter disclosed in thisdocument. The Detailed Description that follows and the Drawings thatare referred to in the Detailed Description will further describe theembodiments described in the Summary as well as other embodiments.Accordingly, to understand all the embodiments described by thisdocument, a full review of the Summary, Detailed Description and theDrawings is needed. Moreover, the claimed subject matters are not to belimited by the illustrative details in the Summary, Detailed Descriptionand the Drawing, but rather are to be defined by the appended claims,because the claimed subject matters can be embodied in other specificforms without departing from the spirit of the subject matters.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the invention are set forth in the appendedclaims. However, for purposes of explanation, several embodiments of theinvention are set forth in the following figures.

FIG. 1 illustrates a configuration view of a logical router, whichrepresents a logical network as designed by a user.

FIG. 2 illustrates a control plane view of a logical network when thelogical router is implemented in a distributed manner.

FIG. 3 illustrates a physical distributed implementation of a logicalrouter defined for a logical network.

FIG. 4 conceptually illustrates a more detailed configuration of alogical network topology, including the network addresses and interfacesassigned by an administrator.

FIG. 5 illustrates the configuration of a logical router and how thecontrol plane configures the tunnel endpoint locators on an MHFE thatimplements the logical router.

FIG. 6 conceptually illustrates a process of some embodiments forconfiguring the tunnel endpoint locators for different ports of thelogical router on an MHFE.

FIG. 7 illustrates the configuration data propagated in differentdatabase tables stored on an MHFE using the OVSDB schema in order toenable the MHFE to infer the data link layer (MAC) address of logicalports of a logical router.

FIG. 8 conceptually illustrates a process that the MHFE of someembodiments performs for identifying logical ports of a logical routerconfigured on the MHFE.

FIG. 9 illustrates a physical network implementation logical router thatroutes the logical network traffic.

FIG. 10 illustrates a control plane view for the physical networkimplementation shown in FIG. 9.

FIG. 11 conceptually illustrates a multi-tier logical router in alogical network of some embodiments.

FIG. 12 illustrates the control plane view for the logical topology ofFIG. 11 when a TLR in the logical network is completely distributed.

FIG. 13 illustrates another example of the configuration data propagatedin different database tables stored on an MHFE using the OVSDB schema inorder to enable the MHFE to infer the MAC address of logical ports ofmulti-tier logical routers.

FIG. 14 illustrates an example of a logical network topology thatincludes single-tier logical router and a RIB that defines the routes ofthe logical router.

FIG. 15 illustrates a control plane view of the logical network topologyof FIG. 14 when the logical router is configured in active-standby mode,rather than active-active (ECMP) mode.

FIG. 16 illustrates another example of the configuration data propagatedin different database tables stored on an MHFE using the OVSDB schema inorder to enable the MHFE to infer the MAC address of logical ports ofthe logical router.

FIG. 17 illustrates a control plane view and physical realization of alogical network topology, in which an edge MHFE implements the servicecomponent of the logical router and communicates with external networksthrough the service component.

FIG. 18 illustrates an example of the configuration data propagated indifferent database tables stored on an MHFE using the OVSDB schema inorder to configure the MHFE as an edge node of the logical router.

FIG. 19 conceptually illustrates an electronic system with which someembodiments of the invention are implemented.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description of the invention, numerousdetails, examples, and embodiments of the invention are set forth anddescribed. However, it should be understood that the invention is notlimited to the embodiments set forth and that the invention may bepracticed without some of the specific details and examples discussed.

A new schema (i.e., OVSDB schema) that allows the control plane toconfigure hardware switches to implement different logical networks (fordifferent tenants) has recently been introduced to the market. Someembodiments provide methods to improve this new schema in order toimplement different logical network elements (e.g., logical routers) onthe hardware switches.

Some embodiments provide a novel method of configuring a logical routerof a logical network on a managed hardware forwarding element (MHFE) inorder for the MHFE to implement the logical network and to performlogical routing functionalities. In some embodiments, the method isperformed by a control plane that configures and manages one or morelogical networks for one or more tenants of a hosting system (e.g., adatacenter). In some embodiments, a logical network of the hostingsystem includes a set of logical forwarding elements (e.g., logicalswitches and routers) that logically connects different end machines(e.g., virtual machines, containers, etc.) that run on different hostmachines.

Some embodiments configure a logical router of a logical network on theMHFE (e.g., a third-party hardware switch such as a top-of-rack (TOR)switch or other appliances such as firewalls, load balancers, etc.) toenable the physical workloads connected to the MHFE (e.g., third-partyservers connected to a TOR switch) to exchange network data with otherend machines and/or external networks that are connected to the logicalnetwork.

In some embodiments, the control plane receives a definition of alogical router (e.g., through an application programming interface(API)) and defines several routing components for the logical router.Each of these routing components is separately assigned a set of routesand a set of logical interfaces. Each logical interface (also referredto as logical port) of each routing component is also assigned a networklayer (e.g., Internet Protocol (IP)) address and a data link layer(e.g., media access control (MAC)) address. In some embodiments, theseveral routing components defined for a logical router include a singledistributed router (also referred to as distributed routing component)and several different service routers (also referred to as servicerouting components). In addition, the control plane of some embodimentsdefines a transit logical switch (TLS) for handling communicationsbetween the components internal to the logical router (i.e., between thedistributed router and the service routers).

The service components of a logical router, in some embodiments, may beconfigured in active-active or active-standby mode. In active-activemode, all of the service components are fully functional at the sametime, and traffic can ingress or egress from the logical network throughthe service components using equal-cost multi-path (ECMP) forwardingprinciples (balancing the traffic across the various service routingcomponents). In this mode, each logical interface of each separateservice component has unique IP and MAC addresses for communicating withan external network and/or with the distributed component (through thetransit logical switch).

In some embodiments, the logical router is part of a two-tier logicalnetwork structure. The two-tier structure of some embodiments includes(1) a single logical router (referred to as a provider logical router(PLR) and administrated by, e.g., the owner of the datacenter) forconnecting the logical network to a network external to the datacenter,and (2) multiple logical routers (each referred to as a tenant logicalrouter (TLR) and administrated by, e.g., different tenants of thedatacenter) that connect to the PLR and do not separately communicatewith the external network. In some embodiments, the control planedefines a transit logical switch between the distributed component ofthe PLR and the service components of the TLR.

For a PLR logical router, some embodiments use active-active modewhenever possible, and only use active-standby mode when statefulservices (e.g., NAT, firewall, load balancer, etc.) are configured forthe PLR. In active-standby mode, only one of the service routingcomponents is active, i.e., fully operational at a time, and only thisactive routing component sends out messages to attract traffic. All theother service routing components is in standby. In some embodiments, theactive service component and a standby service component use the same IPaddress, but different MAC addresses, for communicating with thedistributed component. However, only the active component replies toaddress resolution protocol (ARP) requests from this distributedcomponent. Furthermore, only the active service component advertisesroutes to the external network to attract traffic.

For a TLR logical router, some embodiments either use no servicecomponents or two service components in active-standby mode whenstateful services are configured for the TLR. The TLR operatesinternally in the same manner as a PLR in active-standby mode, i.e.,having an active component and a standby component sharing the samenetwork layer address, but only the active component responding to ARPrequests. To connect to the PLR, some embodiments assign each of the twoservice components of the TLR a same network layer address (thoughdifferent from the IP address used to connect to its own distributedcomponent).

The logical router described above is a distributed logical routerimplemented by a single distributed routing component and a set ofservice routing components. Some embodiments provide other types oflogical router implementations in a physical network (e.g., a datacenternetwork) such as a centralized logical router. In a centralized logicalrouter, L3 logical routing functionalities are performed in only gatewaymachines, and the control plane of some embodiments does not define anydistributed routing component and instead only defines multiple servicerouting components, each of which is implemented in a separate gatewaymachine. Different types of logical routers with multiple routingcomponents for end machines of a datacenter are described in greaterdetail in U.S. Provisional Patent Application 62/110,061, filed Jan. 30,2015, which is incorporated herein by reference.

The above introduced the general concepts of a logical routerconfiguration as well as certain aspects of the logical routerconfiguration and implementation of some embodiments. In the following,Section I describes how the different routing components of a logicalrouter is configured on a managed hardware forwarding elements (e.g., aTOR switch) in order for the MHFE to implement these components. SectionII then describes configuring the logical router on the MHFE in such away to enable the MHFE to perform routing functionalities. Next, SectionIII describes configuration of the MHFEs in other types of logicalnetwork topologies and for other types of logical routers. Section IVthen describes configuring an MHFE as an edge node of a logical router.Finally, Section V describes the electronic system with which someembodiments of the invention are implemented.

I. Configuring Logical Router on MHFE

Some embodiments use a distributed logical router implementation thatenables first-hop routing in a distributed fashion (rather thanconcentrating all of the routing functionality at the gateways). In thephysical realization, the logical router of some embodiments includes asingle distributed routing component (also referred to as a distributedrouter (DR)) and one or more service routing components (also referredto as service routers (SRs)). The DR, in some embodiments, spans managedforwarding elements (MFEs) that couple directly with virtual machines(VMs) or other data compute nodes that are logically connected, directlyor indirectly, to the logical router. The DR of some embodiments alsospans the gateways to which the logical router is bound as well as oneor more MHFEs (e.g., third-party physical machines). The DR of someembodiments is responsible for first-hop distributed routing betweenlogical switches and/or other logical routers that are logicallyconnected to the logical router.

The service routers (SRs) of some embodiments are responsible fordelivering services that are not implemented in a distributed fashion(e.g., some stateful services) as well as connecting the logical networkto external network(s). A distributed logical router will have SRs ifeither (i) the logical router is a provider logical router (PLR), andtherefore connects to external physical networks or (ii) the logicalrouter has services configured that do not have a distributedimplementation (e.g., NAT, load balancing, DHCP in some embodiments).Even if there are no stateful services configured on a PLR, someembodiments use SRs for failure handling and for ECMP.

Logical routers, in some embodiments, can be viewed from three differentperspectives. The first of these views is the API view, or configurationview, which is how the user (e.g., a datacenter provider or tenant)views and defines the logical router. The second view is the controlplane or management plane view, which is how the controller computerinternally defines the logical router. Finally, the third view is thephysical realization, or implementation of the logical router, which ishow the logical router is actually implemented in the physical network.

FIG. 1 illustrates the configuration view of a distributed logicalrouter in a logical network as designed by a user (e.g., a networkadministrator, a tenant of a datacenter, etc.). As shown, the logicalrouter 115 is part of the logical network 100 which also includes twoother logical switches 105 and 110. The logical router 115 has twological ports that are connected to the logical switches 105 and 110.

Logical switch 105 has logical ports that are connected to virtualmachines VM1 and VM2 while the logical switch 110 has logical portsconnected to the virtual machine VM3 and TOR switch 130. The logicalrouter 115 also includes two logical ports that connect to the externalphysical network 120. The TOR switch 130 connects one or more physicalmachines (e.g., physical servers, etc.) to the VMs of the logicalnetwork 100 through the logical switches 105 and 110, and the logicalrouter 115.

While shown as VMs in this figure and other figures below, it should beunderstood that other types of data compute nodes (e.g., namespaces,containers, etc.) may connect to logical forwarding elements (e.g.,logical switches 105 or logical routers 115) in some embodiments. Itshould also be understood that although a TOR switch in the examplefigures is shown as a managed hardware forwarding element (MHFE), theMHFE can be any other third-party forwarding elements (e.g., otherphysical switches and routers, appliances such as firewalls, loadbalancers, etc.). Additionally, although in the illustrated example, aswell other examples below, only one TOR switch is shown to connect tothe logical network, one of ordinary skill in the art would realize thatmany more TOR switches or other third-party hardware switches canconnect to the logical network in the same manner. The illustratedexamples include only one TOR switch in order to simplify the figuresand the descriptions.

FIG. 2 illustrates the management (control) plane view of the logicalnetwork 100 shown in FIG. 1. The control plane view 200 for thedistributed implementation illustrates that the control plane, afterreceiving the configuration data of the distributed logical router,creates a distributed router 220, two service routers 230 and 240, and atransit logical switch 210 based on the received logical router data. Insome embodiments, the control plane generates separate routinginformation bases (RIBs) and/or forwarding information bases (FIBs) foreach of the routing components 220, 230, and 240. That is, in additionto having separate objects created in the management/control plane, eachof the routing components is treated as a separate router with separateroutes.

The transit logical switch 210 has different logical ports for each ofthe created routers, and each of the routing components 220-240 has aninterface to logically connect to the transit logical switch 210. Theconfiguration of the northbound and southbound interfaces of the variousrouting components 220-240 and their connections with the transitlogical switch 210 will be described in further detail below byreference to FIGS. 3 and 4.

FIG. 3 illustrates the physical distributed implementation of thelogical router 115 of FIG. 1. As shown, the virtual machine VM1, whichcouples to the logical switch 105 (LS1) in the logical network 100,operates on the host machine Host1, while VM2 and VM3 that couple tological switches 105 and 110, respectively, operate on the host machineHost2. Additionally, the TOR switch 130 that couples to the logicalswitch 110 is part of a third-party rack 310 which also includes a setof servers 320 that are connected to the TOR switch 130. The virtualmachines VM1-VM3 and servers 320 communicate (e.g., exchange networkdata) with each other and other entities via the logical network 100.

Each host machine is operating a managed forwarding element (MFE) 315.In some embodiments, the MFEs 315 operating on the host machines aresoftware switches provided by the hypervisors or other virtualizationsoftware on the host machines. The TOR 130 is operating as a managedhardware forwarding element (MHFE). A MHFE in some embodiments is athird-party hardware switch that implements one or more logical networksand logically connects the physical workload attached to it (e.g.,hardware and physical machines connected to the TOR 130) to the endmachines and other devices in the logical network. The MFEs and MHFEimplement the logical switches 105, 110, and 210 as well as thedistributed routing component 220. The MFEs of some embodiments performfirst-hop switching for the logical switches 105 and 110 for packetssent by the VMs of the logical network 100 (unless the pipeline of thetransit logical switch 210 of the MFE specifies to send the packet to aSR). The MFEs 315 (or a subset of them) may also implement logicalswitches (and distributed logical routers) for other logical networks ifthe other logical networks have VMs that reside on the host machinesHost1 and Host2 as well.

The control plane of some embodiments configures and manages one or morelogical networks for one or more tenants of a hosting system (e.g., adatacenter). In some embodiments, a logical network of the hostingsystem logically connects a set of end machines (e.g., virtual machines,physical servers, containers, etc.) and a set of physical machines usinga set of logical forwarding elements (e.g., logical L2 and L3 switches).In some embodiments, different subsets of end machines reside ondifferent host machines that execute managed forwarding elements (MFEs).The MFEs implement the logical forwarding elements of the logicalnetwork to which the local end machines are logically connected. TheseMFEs may be flow-based forwarding elements (e.g., Open vSwitch) orcode-based forwarding elements (e.g., ESX), or a combination of the two,in various different embodiments. These different types of forwardingelements implement the various logical forwarding elements differently,but in each case they execute a pipeline for each logical forwardingelement that may be required to process a packet.

In some embodiments, the logical forwarding elements are implemented byone or more MHFEs (e.g., TOR switches) in order to connect the physicalmachines that are connected to the MHFEs to the other end machines ofthe logical network. In other words, each of the host machines executesan MFE that processes packets sent to and received from the end machinesresiding on the host machine, and exchanges these packets with otherMFEs operating on other host machines as well as the MHFEs (e.g.,through tunnels established by overlay encapsulation).

In some embodiments, when the MFE receives a packet from a VM that iscoupled to the MFE, it performs the processing for the logical switch towhich that VM logically couples, as well as the processing for anyadditional logical forwarding elements (e.g., logical router processingif the packet is sent to an external network, logical router processingand processing for the other logical switch in the network if the packetis sent to an end machine coupled to the other logical switch, etc.).

In some embodiments, the MFEs implement the logical forwarding elementsthrough a set of flow entries. These flow entries are generated by alocal controller operating on each host machine (not shown). The localcontroller of each host machine generates the flow entries by receivingthe logical forwarding data from the control plane and converting thelogical forwarding data to the flow entries for routing the packets ofthe logical network in the host machine. That is, the local controller,operating on a host machine, converts the universal logical forwardingdata that is computed and sent by the control plane to every localcontroller operating on different host machines, to a customized set offorwarding behaviors that is recognizable and used by the MFE thatoperates on the same host machine as the local controller.

The MFE then uses the customized set of forwarding data to forward thepackets of the logical network between the end machines operating on thehost machine. In other words, by using the generated flow entries, theMFEs are able to forward and route packets between network elements ofthe logical network that are coupled to the MFEs. In some embodiments,however, some or all of the MFEs are not flow-based software forwardingelements, but instead process packets based on configuration data thatis generated by their respective local controllers. In some embodiments,the local controllers receive the same data from the control planeirrespective of the type of MFEs they manage, and perform different dataconversions for different types of MFEs.

Additionally, the control plane distributes the logical forwarding dataof the logical forwarding elements to the TOR switch 130 in order forthe TOR switch to implement these logical forwarding elements andconnect the physical workload to the virtual machines VM1-VM3. In someembodiments, the control plane distributes the logical forwarding dataof the logical forwarding elements to the TOR switch using an opensource database schema such as OVSDB. In some other embodiments thecontrol plane distributes the forwarding data to a particular MHFEcontroller using the NETCPA protocol, which is a proprietary protocol (aVXLAN control plane protocol). In some such embodiments, the MHFEcontroller subsequently translate the logical forwarding data to theopen source protocol that is recognizable by the TOR switch anddistributes the forwarding data to the TOR switch using the open sourceprotocol.

The distributed router 220, as shown in FIG. 3, is implemented acrossthe MFEs 315, the TOR switch 130, and the gateway machines 330 and 335.That is, the datapaths (e.g., in the MFEs 315, or in a different formfactor on the gateways and MHFEs) all include the necessary processingpipelines for the DR 220 (and the transit logical switch 210 illustratedin FIG. 2). Unlike the distributed router 220, each of the two servicerouters 230 and 240 operates on a single gateway machine. Specifically,the SR 230 shown in the figure operates on the gateway machine 330,while the SR 240 operates on the gateway machine 335.

In some embodiments, the gateway machines 330 and 335 (also called edgenodes in some embodiments) are host machines similar to the hostmachines Host1 and Host2, which host service routers rather than userVMs. As shown in the figure, each of the gateway machines 330 and 335includes an MFE 315 as well, which are similar to the other MFEsoperating on the other host machines that implement the logicalforwarding elements of the logical network 100. In the illustratedgateway machines 330 and 335, the SRs are shown as separate from theMFEs that operate on the gateway machines.

Different embodiments, however, may implement the SRs differently. Someembodiments implement the SRs as VMs (e.g., when the MFE is a softwareswitch integrated into the virtualization software of the gatewaymachine), in which case the SR processing is performed outside of theMFE. As will be discussed in more detail below in Section IV, someembodiments implement the SRs on an edge MHFE (e.g., a hardware VTEP).In some such embodiments, the edge hardware VTEP plays the role of agateway machine and connects the logical network (also implemented bythe VTEP) to external network(s).

On the other hand, some embodiments implement the SRs as virtual routingand forwarding (VRFs) elements within the MFE datapath (when the MFEuses DPDK for the datapath processing). In either case, the MFE treatsthe SR as part of the datapath, but in the case of the SR being a VM (orother data compute node) separate from the MFE, the MFE sends the packetto the SR for processing by the SR pipeline (which may include theperformance of various services). As with the MFEs on the host machinesHost1 and Host2, the MFEs of the gateway machines, as described above,are configured to perform all of the distributed processing componentsof the logical network.

The SRs of some embodiments may operate in an active-active oractive-standby mode, depending on whether any stateful services (e.g.,firewalls) are configured on the logical router. When stateful servicesare configured, some embodiments require only a single active SR. Insome embodiments, the active and standby service routers are providedwith the same configuration, but the MFEs operating on the host machinesare configured to send packets via a tunnel to the active SR (or to theMFE of the gateway machine that implements the active SR). Only if thetunnel is down will the MFE send packets to the standby SR.

As described above, in order to exchange the network data between thedifferent elements of the logical network 100, the different MFEs andMHFE that implement the logical forwarding elements establish tunnelsbetween themselves. In some embodiments, the control plane (e.g., one ormore controller computers of a centralized controller system)distributes configuration data to the MFEs and MHFE (e.g., throughseparate controllers of MFEs and MHFE), which includes instructions onhow to set up tunnels between the MFEs and MHFE. For instance, theconfiguration data specifies the location (e.g., IP address) of eachtunnel endpoint. In some embodiments, the TOR switch is also one of thetunnel endpoints.

The TOR switch of some embodiments, after receiving the endpointaddresses (in the configuration data), stores the tunnel endpointaddresses of the other MFEs and MHFEs that implements the logicalforwarding elements and their different logical ports in a particulartunnel endpoint locator table. The tunnel endpoint locator table is oneof several database tables that are configured on the TOR switch througha database schema (e.g., OVSDB). The distributed configuration data,therefore, enables the TOR switch to locate other tunnel endpoints(through their IP addresses) and establish the tunnels between the TORswitch and the other endpoints. Configuring the TOR switch to enable theswitch to locate these other endpoints is discussed in further detailbelow.

When a user configures a logical router, the control plane uses thisconfiguration to configure the SRs and the DR of the logical router. Forinstance, the logical router 115 of FIG. 1 has four interfaces (twoports connected to the logical switches' ports, and two uplink ports).However, as shown in FIG. 2, the distributed control planeimplementation of the logical router includes a DR with three logicalports (two of which are connected to the logical switches and oneconnected to the TLS 210) and two SRs that each has two logical ports (atotal of seven interfaces). The IP and MAC addresses and otherconfiguration details assigned to the four interfaces as part of thelogical router configuration are used to generate the configuration forthe various components of the logical router.

In addition, as part of the configuration, some embodiments generate arouting information base (RIB) for each of the logical routercomponents. That is, although the administrator defines only a singlelogical router, the management (control) plane of some embodimentsgenerates separate RIBs and/or FIBs for the DR and for each of the SRs.For the SRs of a PLR, the control plane in some embodiments generatesthe RIB initially, but the physical implementation of the SR also runs adynamic routing protocol process (e.g., BGP, OSPF, etc.) to supplementthe RIB locally.

In some embodiments, the DR is always located on the southbound side(i.e., facing the data compute nodes of the logical network, rather thanfacing the external physical network) of the logical routerimplementation. The southbound ports of the DR, therefore, are connectedto different logical switches that have their other ports connected todifferent virtual and physical machines that reside in host machines orconnected to managed hardware forwarding elements, or alternatively havetheir ports connected to other forwarding elements. The northboundinterface of the DR, on the other hand, couples to the transit logicalswitch that is part of the logical router.

FIG. 4 conceptually illustrates a detailed configuration of a logicalnetwork topology 400 that includes the network addresses and interfacesassigned by a user. As shown, the logical switches 405 and 410 are eachassigned their own subnets, 1.1.1.0/24 and 1.1.2.0/24, and all of thedata compute nodes and MHFEs attached to the logical switches 405 and410 have IP addresses in the corresponding subnet. The logical router415 has an interface L1 to the first logical switch 405. The interfaceL1 has an IP address of 1.1.1.253 that is the default gateway for thedata compute nodes and MHFEs in the subnet 1.1.1.0/24, which includesthe VM 490. The logical router 415 also has a second interface L2 to thesecond logical switch 410. The interface L2 has an IP address of1.1.2.253 that is the default gateway for the data compute nodes andMHFEs in the subnet 1.1.2.0/24, which includes the TOR switch 495.

The northbound side of the logical router 415 has two uplinks, U1 andU2. The first uplink U1 has an IP address of 192.168.1.253 and connectsto a first physical router 420 with an IP address of 192.168.1.252. Thesecond uplink U2 has an IP address of 192.168.2.253 and connects to asecond physical router 425 with an IP address of 192.168.2.252. Thephysical routers 420 and 425 are not actually part of the logicalnetwork (e.g., logical network 100), but rather connect the logicalnetwork to the external networks 430 and 435. The first physical router420 connects to the subnet 10.0.0.0/8, while the second physical router425 connects to both of the subnets 10.0.0.0/8 and 11.0.0.0/8. Althoughnot shown, each of the logical ports of the logical router 415 is alsoassigned a separate data link layer (MAC) address.

Based on these example addresses, the RIB 450 defines the differentroutings performed by the router 415. Specifically, the RIB includesfour connected routes based on the subnets configured on the southboundand northbound interfaces of the logical router. These four connectedroutes include a route that egresses from logical port L1 for any packetthat has a destination IP address that is in the subnet of LS1; a routethat egresses from the logical port L2 for packets with destination IPaddresses that belong to the subnet of LS2; a route that egresses thelogical port U1 for packets with destination IP addresses that belong tothe subnet of U1 and/or physical router 420; and a route that egressesfrom the logical port U2 for packets with destination IP addresses thatbelong to the subnet of U2 and/or physical router 425. The RIB alsoincludes three other static routes: any packet with the subnet IPaddress of 10.0.0.0/8 is to be routed from either logical port U1 orlogical port U2; any packet with the subnet IP address of 11.0.0.0/8 isto be routed from logical port U2; and a default route which is eitherthrough the logical port U1 or the logical port U2 of the router.

FIG. 5 illustrates the configuration of the logical router 415 of FIG. 4and how the control plane configures the tunnel endpoint locators on anMHFE that implements the logical router 415. As shown, the logicalswitches 405 and 410 are configured as indicated by the userconfiguration. However, the control plane defines a distributed routingcomponent (DR) 505, two service routing components (SRs) 510 and 515,and a transit logical switch (TLS or L3) 520 for the logical router 415.The DR is assigned the two southbound interfaces of the logical router415, which connect to the logical switches 405 and 410. The transitlogical switch 520 (L3) is assigned a subnet of 192.168.100.0/30. Someembodiments require the subnet assignment of each logical switch beunique among the logical switches that logically connect (directly orindirectly) the logical router 415. Each of the three control planerouter constructs (the DR 505, the SR 510, and the SR 515) also includesan interface that connects to the TLS 520, and has an IP address in thesubnet of the transit logical switch. The northbound interfaces U1 andU2 are assigned to the two SRs 510 and 515, the configuration of whichis described below.

A DR (e.g., 505) of a logical router (e.g., 415) in some embodiments isconfigured as follows. The southbound interfaces of the DR areconfigured in the same way as the southbound interfaces of the logicalrouter. These interfaces are those that connect to a logical switch inthe logical topology. The DR of some embodiments is allocated a singlenorthbound interface, which is assigned an IP address and a MAC address.Assuming the logical router has one or more SRs, the northboundinterface of the DR connects to a transit logical switch.

The RIB of the DR is assigned connected routes based on the subnetsconfigured on its various southbound and northbound interfaces. Theseare the subnets configured for (i) the transit logical switch configuredbetween the DR and SR components of the logical router, and (ii) anylogical switches on its southbound interfaces. These logical switches onthe southbound interfaces are user-defined logical domains to which datacompute nodes connect (or other transit logical switches located betweenthe DR of a PLR and any TLRs that connect to the PLR as described belowis Section III below).

In addition, any static routes that egress from an uplink of the logicalrouter are included in the RIB of the DR; however, these routes aremodified such that the next-hop IP address is set to that of theuplink's SR. For example, a static route “a.b.c.0/24 via 192.168.1.252”(192.168.1.252 being an address of an external physical network router)is modified to be “a.b.c.0/24 via [IP of SR's southbound interface]”.Static routes that egress from a southbound interface of the logicalrouter, on the other hand, are included in the RIB of the DR unmodified.

The control plane in some embodiments generates the FIB 530 based on theconfiguration data and the RIB of logical router 415 which includes thedifferent routes illustrated in the figure. The illustrated routesinclude three connected routes, for the logical switch domains connectedto the DR (1.1.1.0/24, 1.1.2.0/24, and 192.168.100.0/24). In addition,the subnet on which the first uplink is located (192.168.1.0/24) isreached via the southbound interface of the first SR 510 (IP1), whilethe subnet on which the second uplink is located (192.168.2.0/24) isreached via the southbound interface of the second SR 515 (IP2). Inaddition, three static routes have been added by the user for thelogical router 415, which the control plane automatically modifies forthe DR 505. Specifically, the static routes include the network10.0.0.0/8 via the southbound interface of either of the SRs, and thenetwork 11.0.0.0/8 via the southbound interface of SR2. Lastly, defaultroutes pointing to these same southbound interfaces are included. Asshown, the IP addresses IP1, IP2, and IP3 that are created by thecontrol plane for the ports of the logical router constructs thatinterface the TLS are all in the subnet 192.168.100.0/24.

In addition to configuring the FIB of the DR, the control plane alsoassigns MAC addresses to the DR interfaces in some embodiments. In someembodiments, some or all of the physical routing elements (e.g.,software modules) in the physical network that implement the DRfunctionality only support a single MAC address. In this case, becausethe MAC of a DR port may come from that of a logical router port visibleto users, this imposes requirements on how the control plane allocatesMAC addresses for the logical router ports. Thus, in some embodiments,all DR/SR ports that connect to any logical switch that has user datacompute nodes or SRs must share a common MAC address. In addition, if aDR/SR port is connected to another DR/SR or to a physical network, thisport is assigned a unique MAC address.

Similar to the DR of a logical router, the control plane also configureseach SR of the logical router with a separate FIB and interfaces. Asdescribed above, in some embodiments SRs may deliver services (i.e.,functionalities beyond simply routing, such as NAT, firewall, loadbalancing, etc.) and provide the connection between the logical networkand external physical networks. As shown in FIG. 5, since the logicalrouter 415 has two uplinks, the control plane defines two servicerouters 510 and 515. Each of these SRs is assigned a southboundinterface, with different IP and MAC addresses (as the SRs are in anactive-active configuration). The IP addresses IP1 (for the first SR510) and IP2 (for the second SR 515) are in the subnet 192.168.100.0/30,as is IP3 (the northbound interface of the DR 505).

For each southbound interface of the logical router, some embodimentsadd a route for the corresponding network to the RIB of each SR. Thisroute points to the northbound DR interface as its next-hop IP address.Furthermore, any other routes configured for the logical router thategress from the southbound interface are copied to the SR with the samenorthbound DR interface as the next-hop IP address. On the other hand, astatic route of the logical router that egresses from an uplink (e.g.,U1 or U2) is copied to the FIB of the SR. In addition, the SRs (of atop-level logical router) may learn dynamic routes and place the learneddynamic routes in their FIB (though some embodiments perform thislocally, without involving the centralized controller system in thecontrol plane).

As described above, some embodiments implement the distributed routingcomponent of the logical router in a distributed manner across thedifferent MFEs and the MHFE. Some of these embodiments implement each ofthe service routing components of the logical network on an edge node(e.g., a gateway machine), which is a machine at the edge of the network(e.g., the datacenter network), in order to communicate with one or moreexternal networks. The control plane of some embodiments distributesconfiguration data of the logical forwarding elements to the MFEs in amanner that is different than to the MHFEs.

In some embodiments, the control plane computes and distributes thelogical configuration and forwarding data to each local controller thatoperates on a host machine using a proprietary protocol (e.g., NETCPA).In some such embodiments, the local controller operating on a hostmachine generates a set of forwarding tables for the MFE that runs onthe same host machine and distributes the generated data to the MFE forimplementing the logical forwarding elements of the logical network(e.g., by forwarding the logical network data to other end machinesexecuted on the same host machine, or establishing tunnels to other MFEsand/or MHFEs and forwarding the network data through the establishedtunnels to those MFEs and MHFEs).

In some embodiments, the control plane computes and distributes thelogical configuration and forwarding data to each MHFE using an opensource protocol that is recognizable and used by the MHFE (e.g., an openvSwitch database management (OVSDB) protocol). In some otherembodiments, the control plane distributes the logical network data to aparticular controller that manages the MHFE using a proprietary protocol(e.g., NETCPA) and the particular controller distributes the data to theMHFE using an open source protocol such as OVSDB. The controllers (localcontroller operating on the host machine, particular controller managingthe MHFE, etc.) of some embodiments are applications that areinstantiated on either the host machines or other dedicated controllermachines.

In order to configure and manage the different components of a logicalrouter as well as other logical forwarding elements (e.g., logical L2switches) of a logical network on a MHFE, some embodiments configuresthe MHFE with a set of database tables (e.g., forwarding tables of theforwarding elements) that is populated by using a database schema (e.g.,OVSDB schema) that is recognizable and used by the MHFE. Such an opensource protocol requires minimal software on the MHFE to enable theimplementation of the logical network forwarding elements (e.g., logicalL2 and L3 forwarding elements) in order to communicate with the othermachines connected to the logical network as well as other externalnetworks.

After generating the database tables on the MHFE using the OVSDB schema,some embodiments propagate a particular one of these tables with thephysical locator information of the logical ports of the differentrouting components (i.e., distributed and service routers) of thelogical router. The physical locator information, in some embodiments,specifies the tunnel endpoint locations (e.g., VXLAN tunnel endpoints orVTEPs). This tunnel endpoint locator table (also referred to as aUcast_Macs_Remote table in some embodiments) specifies the network layer(IP) addresses of the MFEs and MHFEs that implement the logical ports oflogical switches to which the machines (e.g., end machines, physicalmachines, etc.) and/or logical ports of the logical routers areconnected. By locating the endpoints, the MFEs and MHFEs are able toestablish tunnels between themselves and exchange the network datathrough the established tunnels. In some embodiments, a MHFE (i.e., aTOR) is also referred to as a hardware VTEP.

FIG. 5 illustrates a tunnel endpoint locator (Ucast_Macs_Remote) table540 that is generated on the TOR switch 590 (e.g., by the OVSDB schema).Each record of the table 540 has several different fields (or tablecolumns) that include (i) a logical switch field 545 that species thelogical switch to which a port of a machine or a logical router isconnected, (ii) a MAC address field 550 that specifies the correspondingMAC address of the port, and (iii) a locator field 555 that specifiesthe IP address of the tunnel endpoint for the corresponding MAC address.The tunnel endpoint locator table is therefore also referred to as atunnel endpoint table.

In order to configure the logical router on this table 540 (i.e.,configure the locator data of the logical ports of the different routingcomponents on the table), some embodiments populate a record for eachlogical port of the distributed routing component in the table in afirst manner and a record for each logical port of the service routingcomponent in a second different manner. For each port of the distributedrouting component (e.g., DR 505) that is connected to a logicalforwarding element (e.g., LS1 405 and LS2 410), some embodimentsgenerate a record and stores (i) in a logical switch field, the logicalswitch to which the port is connected, (ii) in a MAC address field, theMAC address of the port, and (iii) in a locator field, a fixed IPaddress of 127.0.0.1, or the local host. The local host is a loopbackinterface address (127.0.0.1) in networking which can be used to accessthe machine's own network services.

In other words, when the MHFE realizes that the destination MAC addressof a packet belongs to a port of the distributed routing component, theVTEP of the MHFE does not establish a tunnel for routing the packet.This is because the distributed routing component, as described above,is implemented by every single MFE, MHFE, and gateway that participatesin the logical network. As such, a packet whose destination MAC addressis that of the logical router is not required to be routed to any othernode in the network.

Some embodiments, on the other hand, populate the tunnel endpointlocator table with the tunnel endpoint data of each logical port of theservice routing components that is connected to a logical forwardingelement (e.g., an L2 logical switch). That is, for each logical port ofthe SRs, some embodiments store (i) in the logical switch field, thelogical switch to which the port is connected (e.g., the transit logicalswitch to which the southbound port of the service component isconnected), (ii) in the MAC address field, the MAC address of the port,and (iii) in the locator field, the IP address of the tunnel endpointthat implements the logical switch port to which the service componentport is connected (e.g., the IP address of the gateway machine thatimplements the service routing component).

As for the end machines connected to the logical switches, someembodiments store (i) in the logical switch field, the logical switch towhich the end machine's port is connected, (ii) in the MAC addressfield, the MAC address of the port, and (iii) in the locator field, theIP address of the tunnel endpoint that implements the logical switchport to which the end machine is connected (e.g., the IP address of theMFE that implements the port of the logical switch). For instance, thetunnel endpoint locator table 540 shown in the FIG. 5 includes the MACaddress of virtual machine VM1 (MAC-VM) in the MAC address field 550.The port of this virtual machine is connected to the logical port ofswitch LS1 which is stored in the logical switch field 545. Since theMFE is operated by hypervisor HV1 (not shown in the figure), the controlplane stores the IP address of this hypervisor in the locator field 555.

For the different logical ports of the different logical routingconstructs, the tunnel endpoint locator table 540 includes the threedifferent logical switches (LS1, LS2, and LS3) of the logical network inthe logical switch field 545, the MAC addresses of the ports to whichthe logical switches' corresponding ports are connected in the MACaddress field 550, and the locator (IP address) of the MFEs and MHFEsthat implement the corresponding ports in the tunnel endpoint locatorfield 555. As mentioned above though, the control plane configures thetunnel endpoint locator table differently for different routingcomponents of the logical router.

For example, for the MAC address of the logical port L1 of the DR(MAC-L1) which is connected to the logical switch LS1, the control planestores 127.0.0.1 (localhost) as the IP address of the tunnel endpointlocator field 555. As described above, this is because the distributedcomponent of the logical router is implemented by every MFE, MHFE, andgateway of the logical network and as such no tunnel is required to beestablished for any port of the DR. Therefore, MAC-L2 and MAC3 which arethe MAC addresses of the other ports of the DR that are connected to thelogical switches LS2 and LS3, respectively, also have the same loopbackIP address of 127.0.0.1 (localhost) stored in their corresponding tunnelendpoint locator field 555.

For the service components of the logical router, however, the controlplane stores the IP addresses of the gateway machines that implement(e.g., through the MFEs that the gateway machines execute) the logicalswitch ports that are connected to the SR ports. That is, the SR portSRP1 with the MAC address MAC1 is implemented by the MFE of the gatewaymachine Gateway1 (not shown in the figure). As such, the control planestores, in the locator field, the IP address of MFE of Gateway1 (thehypervisor on which the MFE runs). Similarly, the logical port SRP2 ofthe service component 515 is connected to a logical port of the TLS 520(LS3). This port is implemented by the gateway machine Gateway2 and assuch the table stores the IP address of this gateway machine (the IPaddress of the hypervisor that implements the logical switch connectedto the SRP2 port).

FIG. 6 conceptually illustrates a process 600 of some embodiments forconfiguring the tunnel endpoint locators for different ports of thelogical router on an MHFE. In some embodiments, process 600 is uses acontrol plane of a datacenter (e.g., a set of modules at a centralizedcontroller that manages the networks of a datacenter). The control planeof some embodiments performs the configuration process and then uses acentralized control plane of the controller to distribute the data tothe MHFE (or to a different controller that manages the MHFE to besubsequently distributed to the MHFE) that implements the configuredlogical router.

As shown, the process 600 begins by receiving (at 605) a specificationof a logical router. The specification of the logical router is based ona user (network administrator, tenant, etc.) input to define the logicalrouter. In some embodiments, this specification includes definitions ofany services the logical router should provide, whether the logicalrouter will be configured in active-active or active-standby mode(though some embodiments automatically use active-active mode unlessstateful services are configured), how many uplinks are configured forthe logical router, the IP and MAC addresses of the uplinks, the L2 andL3 connectivity of the uplinks, the subnets of any southbound interfacesof the logical router, any static routes for the RIB of the logicalrouter, as well as other data.

The process then defines (at 610) the different routing components ofthe logical router based on the received specification. Specifically,the process defines a distributed router (DR) and a set of servicerouters (SRs) based on the specification of the logical router andassigns different MAC and IP addresses for the different ports of theserouting components. Defining the different routing components andassigning network data link layers addresses to the different ports ofthe routing components is described in greater detail in the U.S.Provisional Patent Application 62/110,061, filed Jan. 30, 2015.Essentially, the process of some embodiments uses the southboundinterface configuration of the logical router for the southboundinterface of the DR. That is, the IP addresses and MAC addresses for thedifferent southbound ports of the DR are those specified for the logicalrouter.

The process 600 also assigns each uplink specified for the logicalrouter to a gateway machine and defines a SR on the gateway machine. Foreach SR, the process uses the configuration for the uplink assigned tothat gateway machine as the configuration for the northbound interfaceof the SR. This configuration information includes the IP and MACaddress of the uplink, as well as any uplink-specific policies. Indefining the different routing components, the process additionallydefines a unique transit logical switch to connect the defined SRs andDR. Some embodiments require that the subnet assigned to the transitlogical switch be unique among the logical network topology. The processalso assigns a northbound interface to the DR and assigns both a MACaddress and an IP address to this interface. The process also assignssouthbound interfaces to the SRs with separate MAC and IP addresses(only the active-standby SRs may share the same IP address). In someembodiments, the IP addresses of the northbound port of the DR and thesouthbound ports of the SRs are in the same subnet that is assigned tothe transit logical switch.

The process 600 receives (at 615) the first defined port (e.g., a portthat is defined for the DR or one of the SRs). This is done in order toconfigure the defined ports of different routing components on the MHFE.The process then determines (at 620) whether the port belongs to adistributed routing component of the logical router or a servicecomponent of the logical router. If the port belongs to the DR, theprocess proceeds to 625. Otherwise, the process proceeds to 635.

At 625, the process stores the localhost as the IP address of the tunnelendpoint. That is, when the process realizes that the port that is beingconfigured on the MHFE one of the southbound ports of the DR or thenorthbound port of the DR, the process stores in the locator field ofthe tunnel endpoint locator table (Ucast_Macs_Remote table) the loopbackIP address 127.0.0.1. As described before, this address indicates to theMHFE that no tunneling is required for the packets that have one of theMAC addresses of the DR ports since DR is implemented on every otherMFE, MHFE, and gateway machines as well. The process then proceeds to630.

At 635, the process determines whether the port is associated with alogical switch. In other words, the process determines whether the portis one of the uplink ports of the SRs that might be directly connectedto a next hop physical router, in which case no logical switch isassociated with to the port. If the process determines that the port isnot associated with a logical switch, the process proceeds to 645. Onthe other hand, when the process determines that the port is associatedwith a logical switch, the process stores (at 640) the IP address of thetransport node (tunnel endpoint) that implements the associated logicalswitch with the SR port before proceeding to 630.

At 630, the process populates the tunnel endpoint table (e.g., 540) withthe information of the DR port in order to configure this port on theMHFE. That is, the process generates a record in the table that has (i)the localhost in the locator field, (ii) the MAC address of the DR portin the MAC address field, and (iii) the logical switch with which thisDR port is associated (i.e., the logical switch to one of the logicalports of which, the DR port is connected) in the logical switch field.As described above, in some embodiments, the logical switches, withwhich the DR ports are associated, might be either one of the southboundlogical switches that logically connect the end machines executing onthe hosts and other physical machines connected to the MHFEs to thelogical router, or alternatively, the transit logical switch with whichthe northbound port of the DR is associated. The process then proceedsto 645.

After populating the tunnel endpoint table with the port information ofthe DR port or one of the SR ports, the process of some embodimentsdetermines (at 645) whether the configured port is the last routingcomponent port that is inspected and configured by the process. If theprocess determines that the port is not the last routing component port,the process receives (at 650) the next routing component port andreturns to 620 to perform all of the above described steps on the port.Otherwise, the process 600 ends.

Some embodiments perform variations of the process 600. The specificoperations of the process 600 may not be performed in the exact ordershown and described. For example, the process of some embodiments, afterdefining each port (and assigning the MAC and IP addresses to the port)for each of the routing components of the logical router, configures thedefined port on the MHFE. In other words, the process of some suchembodiments does not define all the ports of the different routingcomponents before configuring the ports in the manner described above.Additionally, the specific operations may not be performed in onecontinuous series of operations, and different specific operations maybe performed in different embodiments. For example, the operation 610(defining the different routing components and their correspondingports) can be performed in multiple different steps, each step performedunder different conditions (e.g., in an active-standby mode theassignment of the IP and MAC addresses is different than the assignmentof the IP and MAC addresses in an active-active mode).

II. Identifying L3 Packets on MHFE

Some embodiments enable an MHFE (or the hardware VTEP of the MHFE) toperform L3 routing functionalities on the packets that are destined forthe logical router implemented by the MHFE. In order for the hardwareVTEP to realize that a packet is destined for the logical router, thehardware VTEP in some embodiments identifies the destination MAC addressof the packet as a MAC address that belongs to a logical port of arouting component of the logical router. In order to enable the hardwareVTEP to make such a determination, some embodiments use the databaseschema (e.g., OVSDB schema) to propagate configuration data that linksthe different database tables generated on the MHFE.

Linking the different tables allows the hardware VTEP to search the MACaddress of the received packet against a logical router table that hasall the MAC addresses of the different ports of the different routingconstructs of the logical router. In OVSDB schema, among the differenttables (e.g., forwarding tables) that are generated and configured onthe MHFE, the control plane in some embodiments generates a logicalrouter table on the MHFE that maps the IP addresses of the differentports of the distributed and service routing components of the logicalrouter to the logical switches with which they are associated. Incontrast, the tunnel endpoint locator table described above includes theMAC addresses of all the different logical ports of the routingcomponents of the logical router. In order to link the logical routertable and the tunnel endpoint locator table together, some embodimentsstore the IP addresses of the ports of the logical router in an optionalfield of the tunnel endpoint locater table while populating it. In otherwords, the control plane uses a field of the table that may or may notbe used to propagate the linking configuration data.

By doing so, the hardware VTEP of some embodiments would be able toidentify a corresponding IP address for the destination MAC address ofthe packet from the tunnel endpoint locator table and match the IPaddress against the IP addresses of all the logical ports of the routingcomponents that are stored in the logical router table in the OVSDBschema (i.e., the logical router table configured on the MHFE). When thehardware VTEP finds a match for the IP address in the logical routertable, the hardware VTEP realizes that the destination MAC address ofthe packet is in fact a MAC address of one of the logical router ports.As such, the VTEP starts to perform L3 processing on the packet (e.g.,the hardware VTEP modifies the source and destination MAC addresses inthe packet headers to route the packet to the next hop).

FIG. 7 illustrates the configuration data propagated in differentdatabase tables stored on an MHFE using the OVSDB schema in order toenable the MHFE to infer the data link layer (MAC) address of logicalports of a logical router. The MHFE for which the tables are illustratedis the TOR switch 590 shown in FIG. 5. As shown in the figure thelogical router table 710 (Logical_Router table) is a table that isconfigured to map the IP (IPv4 or IPv6) addresses of logical ports of alogical router to one or more logical switches. Since a logical routeris divided to separate distributed and service routers in someembodiments, the control plane of some embodiments configures each ofthese routing components as a separate router in this table. Asillustrated, each record in the logical router table 710 includes an IDfield that identifies the router, a switch binding field that maps thedifferent IP addresses of the different ports of the router to a logicalswitch, and a static route field that specifies the different staticroutes of the router.

As shown, the ID fields includes a row for the distributed router 505(DR) of FIG. 5, a row for the service router 510 (SR1), and a row forthe service router 515 (SR2). The corresponding switch binding field forDR has the IP address of logical port L1 (1.1.1.253/24), which is mappedto the logical switch 405 (LS1). Similarly, the IP address of logicalport L2 (1.1.2.253/24) is mapped to the logical switch 410 (LS2) and theIP address of logical port DRP1 (192.168.100.3/30) is mapped to thetransit logical switch 520 (LS3). The static routes populated in thestatic routes field for the DR are the remaining routes specified in theFIB 530 of the DR. In other words, the connected routes of the FIB ofthe routing component form the switch-binding field of the routingcomponent and the remaining routes in the FIB form the static routesfield in some embodiments.

Therefore, the static routes field of the table 710 shows for the DRthat the subnet on which the first uplink is located (192.168.1.0/24) isreached via the southbound interface of the first SR (IP1), while thesubnet on which the second uplink is located (192.168.2.0/24) is reachedvia the southbound interface of the second SR (IP2). Additionally, thenetwork 10.0.0.0/8 is reached via either of the logical ports SRP1 andSRP2 (e.g., via EMCP), while the network 11.0.0.0/8 is reached via thelogical port SRP2 of the service router SR2. Lastly, the default route(0.0.0.0/0) is reachable via either of the logical ports SRP1 and SRP2(IP1 and IP2).

The table 710 also shows that the switch-binding field for the servicerouting component SR1 maps the IP address of the southbound logical portSRP1 (192.168.100.1/30) to the logical switch LS3. Similarly, theswitch-binding field for the service routing component SR2 maps the IPaddress of the southbound logical port SRP2 (192.168.100.2/30) to thesame logical switch LS3 (the transit logical switch 520 shown in FIG.5). In some embodiments, when there is no logical switch associated withthe northbound logical ports of the service routers (e.g., when theuplinks of the router are connected directly to a physical router thatconnects the router to an external network), no switch binding field forthose logical ports are populated in the logical router table. Finallythe static routes for the two service routers as shown are the remainingroutes of the FIBs of these routers.

The illustrated table 720 is the same tunnel endpoint table 540 shown inFIG. 5 with the exception that this table now shows an additional field760 which is an optional field for holding a corresponding IP addressfor each MAC address populated in field 550 (i.e., the MAC field in theUcast_Macs_Addresses table 540) in the OVSDB schema. As described above,some embodiments (implemented by the control plane) populate the IPaddress of each logical port of the routing components in this field inorder to (1) link the table 720 (i.e., Ucast_Macs_Addresses table) tothe table 710 (Logical Router table) and (2) enable the TOR switch 590to infer the MAC addresses of the logical router ports and therebyidentify the packets that are destined for the logical routerimplemented by the TOR switch.

In some embodiments, the control plane determines which MAC addresses ofthe MAC field belong to a port of a routing component of the logicalrouter during the configuration of the logical router on the MHFE. Thatis, while the control plane is populating the tunnel endpoint locatortable 720 with the IP addresses of each MAC address of a port (e.g.,logical and physical ports of logical and physical switches), thecontrol plane matches the IP address for each port against the IPaddresses stored in the logical router table 710. In some suchembodiments, when a match is found, the control plane tags thecorresponding MAC address in the tunnel endpoint locator table 720 as aMAC address that belongs to a logical router. By doing so, theseembodiments enable the MHFE to infer a MAC address of a received packetbelongs to a logical router port by simply looking up that MAC addressin the tunnel endpoint locator table 720. In other words, when thecontrol plane tags the MAC addresses of the logical router in table 720,the MHFE does not have to (i) retrieve a corresponding IP address foreach MAC address of a received packet and (2) match the retrieved IPaddress against the logical router table.

In some other embodiments, as described above, the control plane tagsthe MAC addresses of the logical ports of a logical router during theconfiguration of the tunnel endpoint locator table. The control planetags these MAC addresses by populating a corresponding IP address foreach MAC address of the table and linking the corresponding IP addressesto the IP addresses of logical ports of the logical router populated inthe logical router table. In some such embodiments, the TOR switchsimply looks up the MAC address of the received packet in the tunnelendpoint locator table 1820 and starts L3 processing on the packet whenthe MAC address of the packet matches one of the tagged MAC addresses inthe table.

As an example, when the TOR switch receives a packet that has adestination MAC address MAC-L1 in the data link layer of the packetheader, the TOR switch concludes that the packet is an L3 packet bysimply looking the MAC address in the tunnel endpoint locator table 720.In some other embodiments though, after extracting the MAC address(e.g., MAC-L1) from the received packet (form the layer 2 header of thepacket), the MHFE retrieves the corresponding IP address for the MACaddress (e.g., IP address 1.1.1.253) from the tunnel endpoint locatortable 720 and matches this IP address against the IP addresses of thelogical router table 710. The TOR switch then realizes that the MACaddress belongs to one of the ports of the DR that is associated withthe logical switch LS1. As such, the TOR switch concludes that thepacket is an L3 packet and starts L3 processing on the packet.

FIG. 8 conceptually illustrates a process 800 that the MHFE (e.g., TORswitch) of some embodiments performs for identifying logical ports of alogical router configured on the MHFE. The illustrated process relatesto the embodiments that configure the tables with the linking data andthe MHFE looks up the corresponding IP address of each MAC address of areceived packet (or the first received packet of a flow) in the logicalrouter table. As described above, in some other embodiments, the controlplane (e.g., a controller computer in a centralized management controlsystem) tags the MAC addresses that belong to the ports of a logicalrouter as L3 MAC addresses while the control plane populates the tunnelendpoint locator table with the linking data.

In some embodiments, in order for the TOR switch to perform the process,the control plane first configures the different tables generated on theTOR switch using OVSDB schema. The control plane, as described above,propagates the different tables is such a way to create a link between afirst forwarding table that contains the MAC addresses of the differentports of the forwarding elements (including the logical router ports),and a second forwarding table that is configured to contain the IPaddresses of the different ports of the logical switch. In order to makesuch a link, the control plane of some embodiments propagates the firstforwarding table with the corresponding IP addresses of every MACaddress that is stored in the table as described above.

The process 800 begins by identifying (at 810) a destination MAC addressof a packet that is received by the TOR switch. The process identifiesthe destination MAC address by extracting the destination MAC addressfield from the data link layer header of the packet in some embodiments.After identifying the MAC address of the packet, the process retrieves(at 820) the corresponding IP address of the MAC address. In someembodiments, the process retrieves the address from a correspondingfield of the tunnel endpoint locator table (e.g., table 720) for thispurpose.

The process then matches (at 830) the retrieved IP address against thelogical router table (e.g., table 710) in order to determine whether arecord with such IP address exists in the table.

Next, the process determines (at 840) whether a match is found for theretrieved IP address in the logical router table. If match is not found,the process 800 ends. If the process is able to find a match anddetermines that the packet is an L3 packet, it tags (at 850) the packetas an L3 packet so the TOR switch routes the packet based on the datastored in the packet headers (e.g., layer 2 and layer 3 headers of thepacket), the routing rules stored in the different RIBs and FIBs of thedifferent routers (e.g., routing components), and the data stored inother forwarding tables (e.g., the tunnel endpoint locator table thatidentifies the location of transport nodes to establish tunnels forexchanging the logical network traffic). The process 800 then ends.

Some embodiments perform variations of the process 800. The specificoperations of the process 800 may not be performed in the exact ordershown and described. For example, the process of some embodiments, afteridentifying (at 810) the destination MAC address of a received packet,do not perform any of the steps 820-840. Some such embodiments simply(i) look up the identified MAC address in the tunnel endpoint locatortable (e.g., table 720 of FIG. 7), and (ii) if the found match in thetable is tagged as an L3 MAC, send the packet for L3 processing.Additionally, the specific operations of process 800 may not beperformed in one continuous series of operations, and different specificoperations may be performed in different embodiments.

The above sections described (1) the configuration of the variouslogical routing components on an MHFE by the control plane in order tolocate the tunnel endpoints for the different ports of the logicalrouting components, and (2) enabling the MHFE to perform routingfunctionalities on the logical network traffic that is destined for thelogical router implemented by the MHFE. An example of routing thelogical network traffic through a logical router implemented by the MHFEis given below. This example is described by reference to FIG. 9, whichis similar to FIG. 3, except that some of the elements of the logicalnetwork are not shown in this figure (e.g., the second host Host2 whichexecutes the second and third virtual machines VM2 and VM3) for thesimplicity of description and to further simplify the provided example.

As described above, the logical routing components (as well as thelogical switches, both those defined by the user and those defined bythe control plane for connecting logical router components) areimplemented by various managed forwarding elements (MFEs) as well as byone or more managed hardware forwarding elements (MHFEs). As shown inFIG. 3, for example, the data compute nodes attached to the user-definedlogical switches reside on physical host machines on which MFEs operate(e.g., within the virtualization software of the host machine), whileother physical machines (e.g., third-party physical machines) areattached to the MHFE (e.g., a third-party hardware switch). The MFEs andMHFE implement the logical switches of a logical network as well as theDRs, in some embodiments.

FIG. 9 illustrates the virtual machine VM1 that resides on the physicalhost machine Host1 that executes managed forwarding element MFE1.Although not shown in this figure, FIG. 2 showed that this virtualmachine is attached to the logical switch 105 (LS1) which is implementedby the MFE 915 (MFE1). The MFE 915 on the physical host machine 910 andthe TOR 590 on the rack 920 include configuration to implement bothlogical switches 105 and 110 (LS1 and LS2), the DR 220, and the transitlogical switch 210. In addition, similar to FIG. 3, this figure showsthat the two gateway machines 330 and 335 (also called edge nodes) eachimplements a SR of the logical router. The figure also shows varioustunnels (e.g., VXLAN tunnels) established between the different MFEs ofthe different host and gateway machines to exchange the network trafficbetween each other. Although not shown in the figure, some embodimentsalso establish a tunnel between the two gateway machine so that the SRsimplemented on these machine can exchange data and in case one of themfails, the other one can take over.

The packet processing pipeline for the example architecture shown inFIG. 9 will now be described by reference to FIG. 10, which is similarto control plane view shown in FIG. 5 with the exception that in thisfigure, the physical port B on TOR switch 590 and port A on VM1 areillustrated. Additionally, this figure includes the same forwardingtables configured on the TOR switch that are shown in FIG. 7 to simplifythe description.

The first example packet processing describes an east-west routing. Insome embodiments, the east-west traffic (e.g., traffic from a datacompute node on LS1 to a data compute node on LS2) is handled primarilyat the first-hop MFE and/or MHFE (e.g., the MFE of the virtualizationsoftware on the host machine 910 for the source VM1), then tunneled tothe destination MFE and/or MHFE (e.g., the MHFE 590 in the rack 920). Assuch, the packets do not pass through the SRs, and thus do not receiveany services provided by these SRs. Other embodiments, however, allowfor routing policies that send certain east-west traffic to the SRs forprocessing.

In the first example a physical machine (e.g., a third-party server)that is connected to the hardware VTEP (i.e., TOR switch 590) sends apacket to the virtual machine VM1 residing on host 910. For thisexample, the different pipelines of different logical forwardingelements implemented by the MHFE is first described. Based on the sourceIP address of the packet (or the ingress port through which the packetis received), the datapath on the MHFE 590 initially runs the sourcelogical switch pipeline, which is logical switch 410 (LS2). The LS2pipeline specifies to forward the packet to the DR 505, the pipeline forwhich also takes place on the MHFE 590. This pipeline identifies thatthe logical switch 405 (LS1) is the next hop based on the destination IPaddress of the packet. As such the source MHFE is not required toestablish a tunnel to any one of the gateway machines that implementsthe SRs, nor does it have to execute the pipeline for the transitlogical switch 520 (LS3).

Instead, the MHFE executes the pipeline for the logical switch LS1 (theidentified next hop), which is also implemented by the MHFE. Thispipeline specifies to tunnel the packet to the MFE that runs on host 910that also executes the destination VM1. That is, the logical switch LS1pipeline identifies the MFE 915 as the MFE that implements the port ofthe logical switch LS1 that is associated with the destination port ofvirtual machine VM1. The logical switch LS1 pipeline then establishes atunnel to this MFE that also executes LS1 pipeline, encapsulates thepacket with appropriate tunneling data and sends the packet to the otherendpoint. Next, the MFE 915 receives the packet, decapsulates it (toremove the tunneling data), and identifies the destination virtualmachine VM1 based on the destination MAC address of the packet. The MFEthen sends the packet to its final destination VM1.

The L3 processing of the packet with example IP and MAC addresses of theports is as follows. In the example, the physical machine is connectedto port B of the hardware VTEP that is associated with the logicalswitch 410 (LS2) as shown in FIG. 10, and has an IP address of IP-B(1.1.2.2) and a MAC address of MAC-B. Also the virtual machine VM1 has avirtual interface (port A), which is implemented on MFE 915. Port A hasan IP address IP-A (1.1.1.1) and a MAC address MAC-A, which isassociated with the logical switch 405 (LS1).

As described above in FIG. 5, the default gateway for the TOR switch 590is the L2 port of the DR 505 (the default gateway has been assigned tothe TOR switch 590 by assigning a static IP address to its differentports including port B, or through a DHCP service). The default gatewayport L2 is in the same subnet as port B is and has an IP address of1.1.2.253 and a MAC address of MAC-L2 as shown in the FIG. 10.Therefore, the physical machine (e.g. a server connected to port B ofthe TOR switch) sends an L3 packet that has a destination MAC address ofMAC-L2, a source MAC address of MAC-B, a destination IP address of1.1.1.1 (i.e. the IP address of VM1), and a source IP address of 1.1.2.2(i.e., the IP address of TOR 590). It should be noted that the MACaddress of the default gateway port can be learned by sending an ARPrequest from the physical machine (e.g., server) connected to port B tothe hardware VTEP, which in response yields the MAC address using theUcast_Macs_Remote table (since the hardware VTEP knows that port B isassociated with the logical switch LS2 and therefore the MAC addressassociated with this logical switch in the table is MAC-L2).

After the packet is received at the hardware VTEP (i.e., TOR 590), thehardware VTEP realizes that the packet is an L3 packet because thedestination MAC address of the packet is MAC-L2 which is a MAC addressof one of the ports of the logical router. As described above, thehardware VTEP makes such a determination by linking the packet's IPaddress to the IP address of the logical router ports in the logicalrouter table 1070 configured on the hardware VTEP. As such, the MHFEperforms L3 processing on the packet. That is, the MHFE replaces thedestination MAC address of the packet (MAC-L2) with the destination MACaddress of the MFE port associated with the virtual machine VM1 (MAC-A)and also replaces the source MAC address MAC-B with the router port'sMAC address (MAC-L1). The source and destination IP addresses remain thesame.

In order to replace the source MAC address, the MHFE looks at the switchbinding column of the logical router table 1070. Based on thedestination IP address of the packet (i.e., 1.1.1.1), the MHFE 590determines that the egress port should be in the same subnet thatlogical switch LS1 is. Therefore the packet must egress from port L1 ofthe DR 505, which has the MAC address of MAC-L1. The MHFE also looks upthe destination IP address in the tunnel endpoint locator table and thematched record in this table yields the MAC address of the MFE port(MAC-A) as well as the tunnel endpoint locator address of the MFE (e.g.,the IP address of the MFE 915 or the IP address of the hypervisor onwhich the MFE runs) that implements the logical switch associated withthis port.

The MHFE 590 then establishes the tunnel 930 (e.g., a VXLAN tunnel) tothe identified tunnel endpoint (MFE 915) and sends the packet to thedestination port using the tunnel (e.g., after adding the tunnelencapsulation data to the packet). In the described example, the MHFE isable to locate the destination MAC address and tunnel endpoint locatorin the tunnel endpoint locator table 1080 based on the destination IPaddress of the packet which is stored in the optional IP address columnof the table at the configuration time of the table (as describedabove). However, if this IP address is missing in the table, someembodiments identify this IP address and store the identified address inthe table using an address resolution protocol (ARP) mechanism.

A second packet processing example which involves north-south routingwill now be described. This example is also described by reference toFIGS. 9 and 10. Specifically, the same machine on port B of the TORswitch sends a northbound packet to a machine in an external network,which has an IP address of 10.10.10.10. For this example, the differentpipelines of different logical forwarding elements implemented by theMHFE is first described. Based on the source IP address of the packet(or the ingress port through which the packet is received), the datapathon the MHFE 590 initially runs the source logical switch pipeline, whichis the logical switch 410 (LS2). The LS2 pipeline specifies to forwardthe packet to the DR 505, the pipeline for which also takes place on theMHFE. This pipeline identifies one of the SRs implemented on a gatewaymachine as its next hop since the subnet of the destination IP addressis shared with both SR subnets (some embodiments use ECMP to select oneof the SRs).

Next, the source MHFE executes the pipeline for the transit logicalswitch 520 (LS3), which specifies to tunnel the packet to theappropriate gateway machine (edge node) that hosts (implements) theselected SR (e.g., one of the gateway machines 330 and 335 in FIG. 9).The gateway machine (i.e., the MFE on the gateway machine) receives thepacket, decapsulates it (to remove the tunneling data), and identifiesthe SR based on the logical context information on the packet (e.g., theVNI of the transit logical switch 520) as well as the destination MACaddress that corresponds to the SR's southbound interface. The SRpipeline is then executed (by the MFE in some embodiments, and by a VMimplementing the SR in other embodiments). The SR pipeline sends thepacket to the physical network that has the destination IP address.

The L3 processing of the packet with example IP and MAC addresses of theports is as follows. Similar to the first example, the physical machineis connected to port B of the hardware VTEP that is associated with thelogical switch LS2 and has an IP address of 1.1.2.2 and a MAC address ofMAC-B. Also as stated before, the packet is being sent to a machine withIP address of 10.10.10.10 in an external network.

As described above, the default gateway for the TOR switch is the L2port of the DR 505. The default gateway port L2 is in the same subnet asport B is and has an IP address of 1.1.2.253 and a MAC address ofMAC-L2. Therefore, the physical machine (on port B of the TOR switch)sends an L3 packet that has a destination MAC address of MAC-L2, asource MAC address of MAC-B, a destination IP address of 10.10.10.10,and a source IP address of IP-B. After the packet is received at thehardware VTEP, the VTEP realizes that the packet is an L3 packet becausethe destination MAC address of the packet is MAC-L2, which is a MACaddress of one of the ports of the logical router (similar to the firstexample described above). As such, the MHFE performs L3 processing onthe packet.

The MHFE 590 starts to perform the L3 processing by replacing thedestination MAC address of the packet (MAC-L2) with the destination MACaddress of any of the SRP1 and SRP2 ports of any of the SR1 and SR2(shown in FIG. 10) associated with the transit logical switch LS3. TheMHFE also replaces the source MAC address MAC-B with the MAC address ofnorthbound logical port of the DR 505 (i.e., MAC3). The source anddestination IP addresses remain the same.

In some embodiments the hardware VTEP (MHFE) decrements the time to live(TTL) field of the packet header in an east-west routing (i.e., whenonly the DR port of the logical router performs the routing such as therouting in the first example). The hardware VTEP of some suchembodiments, however, does not decrement the TTL at the DR routing levelwhen both the distributed routing component and service routingcomponent of the logical router participate in the routing of the packet(as in this example). This is because the TTL should not be decrementedtwice when in fact only one logical router performs the routing process.That is, even though two routing components are participating therouting of the packet in this example, these two components belong to asingle logical router and as such act as one router. In someembodiments, the TTL is decremented at the SR routing level (andtherefore only once).

In order to replace the source MAC address, the MHFE looks at the staticroute field of the logical router table 1070 and based on thedestination IP address of the packet (i.e., 10.10.10.10) determines thatthe egress port should be sent to either SRP1 or SRP2. Therefore thepacket must egress from port DRP1 of the DR 505, which has the MACaddress of MAC3. The hardware VTEP may choose SRP1 or SRP2 as the nexthop using an ECMP algorithm (e.g., based on the hash of the packetheader the hardware VTEP may choose the next hop as SRP1 or SRP2).

The MHFE also looks up the destination IP address in the tunnel endpointlocator table 1080 and the matched record in this table yields both ofthe southbound logical port of the SR (either MAC1 or MAC2) as well asthe tunnel endpoint locator address of the gateway machine thatimplements the logical switch (i.e., transit logical switch LS3 520)associated with this port (i.e., the IP address of either gatewaymachine Gateway 1 or gateway machine Gateway 2 which are implementingthe transit logical switch). The MHFE then establishes the VXLAN tunnel935 or 940 (depending on which SR is chosen) to the identified tunnelendpoint (e.g, an MFE operating on one of these two gateway machines ifthe SR is implemented by the MFE) and sends the packet to thedestination port using the VXLAN tunnel (e.g., after adding the tunnelencapsulation data to the packet).

In the above second example, similar to the first example, the MHFE wasable to locate the destination MAC address and tunnel endpoint locatorin the tunnel endpoint locator table 1080 based on the destination IPaddress of the packet. The destination IP address is stored in theoptional IP address field of the table at the time when the table ispopulated. However, if this IP address is missing in the table, someembodiments identify this IP address by using an address resolutionprotocol (ARP) mechanism and store the identified address in the table.

III. Two Tier and Active-Standby Logical Routers

The above two sections described configuration and implementation of asingle tier logical router that operates in an active-active mode on aMHFE (e.g., a third-party TOR switch). For logical networks withmultiple-tier logical routers, some embodiments include both DRs and SRsat each level, or DRs and SRs at the upper level (the provider logicrouter (PLR) tier) with only DRs at the lower level (the tenant logicalrouter (TLR) tier). FIG. 11 conceptually illustrates a multi-tierlogical router in a logical network 1100 of some embodiments, with FIG.12 illustrating the control plane view of the logical router. Theprovided examples and figures describe a two-tier logical router thatincludes a DR and a set of SRs at the upper level (PLR tier) with only aDR at the lower level (TLR tier). The multiple-tier logical routers thatinclude both DRs and SRs at each level are described in the U.S.Provisional Patent Application 62/110,061, filed Jan. 30, 2015.

FIG. 11 conceptually illustrates a logical network 1100 with two tiersof logical routers. As shown, the logical network 1100 includes aprovider logical router 1105 and several tenant logical routers1110-1120 for L3 operations. The first tenant logical router 1110 hastwo logical switches 1125 and 1130 attached, with one or more datacompute nodes (VMs) and/or MHFEs (TORs) coupling to each of the logicalswitches. For simplicity, only the logical switches attached to thefirst TLR 1110 are shown, although the other TLRs 1115 and 1120 wouldtypically also have attached logical switches (with DCNs and MHFEs). Asan example the figures shows that a virtual machine 1135 has coupled tothe software switch 1125, while a TOR switch 1140 has coupled to thelogical switch 1130.

In some embodiments, any number of TLRs may be attached to a PLR such asthe PLR 1105. Some datacenters may have only a single PLR to which allTLRs implemented in the datacenter attach, whereas other datacenters mayhave numerous PLRs. For instance, a large datacenter may want to usedifferent PLR policies for different tenants, or may have too manydifferent tenants to attach all of the TLRs to a single PLR. Part of therouting table for a PLR includes routes for all of the logical switchdomains of its TLRs, so attaching numerous TLRs to a PLR creates severalroutes for each TLR just based on the subnets attached to the TLRs. ThePLR 1105, as shown in the figure, provides a connection to the externalphysical network 1180 (through the physical router 1170). Someembodiments only allow the PLR to provide such a connection, so that thedatacenter provider can manage this connection. Each of the separateTLRs 1110-1120, though part of the logical network 1100, are configuredindependently (although a single tenant could have multiple TLRs if theyso chose).

As shown in the figure, the logical switches 1125 and 1130 are eachassigned its own subnet, 1.1.1.0/24 and 1.1.2.0/24, and all of the datacompute nodes and MHFEs attached to these logical switches will have IPaddresses in the corresponding subnet. The TLR 1110 has an interface L1to the first logical switch 1125, with an IP address of 1.1.1.253 thatis the default gateway for the data compute nodes and MHFEs in thesubnet 1.1.1.0/24, including the VM 1135. The TLR 1110 also has a secondinterface L2 to the second logical switch 1130, with an IP address of1.1.2.253 which is the default gateway for the data compute nodes andMHFEs in the subnet 1.1.2.0/24, including the TOR switch 1140.

The northbound side of the TLR 1110 has a northbound interface D1 withan IP address of 2.0.0.1 that is connected to the southbound interfaceD2 of the PLR 1105 with an IP address of 2.0.0.0. The PLR 1105 also hasan uplink U1 that is the interface of the PLR to the next hop physicalrouter 1170 with an IP address of 192.168.1.252. The uplink U1 has an IPaddress of 192.168.1.253 and connects to the external network 1180. Thephysical router 1170 is not actually part of the logical network 1100,but rather connect the logical network to the external network 1180.Although not shown, each of the logical ports of the TLR and PLR is alsoassigned a separate data link layer (MAC) address.

Based on these example addresses, the RIB 1150 defines the differentroutes of the TLR 1110. Specifically, the RIB 1150 includes threeconnected routes based on the subnets configured on the southbound andnorthbound interfaces of the TLR 1110. These three connected routesinclude a route that egresses from logical port L1 for any packet thathas a destination IP address that is in the subnet of LS1; a route thategresses from the logical port L2 for packets with destination IPaddresses that belong to the subnet of LS2; and a route that egressesfrom the logical port D1 for packets that are routed to the logical portD2 of the PLR 1105. The RIB 1150 also includes a static default route(e.g., configured by the user) that says any other packets should berouted through the southbound ports of the PLR 1105 (e.g., port D2).

The RIB 1160 of the PLR 1105 does not show the routes that are relatedto any TLR other than the TLR 1110 for simplicity of the description.Specifically, the RIB 1160 includes two connected routes and threestatic routes. The connected routes are based on the subnets configuredon the southbound and northbound interfaces of the PLR (excluding thesouthbound ports that are connected to the other TLRs as stated above).These two connected routes include a route that egresses from logicalport D2 for any packet that is sent to the northbound port of the TLR(D1), and a route that egresses from the logical port U1 for packetswith destination IP addresses that belong to the subnet of U1 and/orphysical router 1170. The RIB also includes three other static routes: aroute that says any packet with the subnet IP address of 1.1.1.0/24should be routed via logical port D1; a route that says any packet withthe subnet IP address of 1.1.2.0/24 should be routed via logical portD1; and finally a default route which is through the physical router1170.

FIG. 12 illustrates the control plane view 1200 for the logical topology1100. The figure also illustrates how the control plane configures thetunnel endpoint locators on an MHFE that implements the logical router.For simplicity, only details of the first TLR 1110 are shown; the otherTLRs will each have its own DR, as well as SRs in some cases. Also tosimplify the description, only one uplink connects the logical networkto an external network. In this example, the PLR 1105 includes a DR 1205and one SR 1210, connected together by a transit logical switch 1225. Inaddition to the transit logical switch 1225 within the PLR 1105implementation, the control plane also defines separate transit logicalswitches between each of the TLRs and the DR 1205 of the PLR 1105, forwhich only the transit switch 1230 (LS4) that is between TLR1 1110 andthe PLR 1105 is shown in the figure.

The transit logical switch 1230 (LS4) connects to a DR 1245 thatimplements the configuration of the TLR 1110. Thus a packet sent to adestination in the external network by a data compute node attached tothe logical switch 1125 (e.g., virtual machine VM1) will be processedthrough the pipelines of the logical switch 1125, the DR 1245 of TLR1110, the transit logical switch 1230, the DR 1205 of the PLR 1105, thetransit logical switch 1225, and the SR 1210 (in the same manner thatdescribed in the two examples described above by reference to FIG. 9).In some embodiments, the existence and definition of the transit logicalswitches 1225 and 1230 are hidden from the user that configures thenetwork through the API (e.g., an administrator), with the possibleexception of troubleshooting purposes.

The above figure illustrates the control plane view of logical routersof some embodiments. In some embodiments, an administrator or other userprovides the logical topology (as well as other configurationinformation) through an API. This data is provided to a control plane,which defines the implementation of the logical network topology (e.g.,by defining the DRs, SRs, transit logical switches, etc.). In addition,in some embodiments a user associates each logical router (e.g., eachPLR or TLR) with a set of physical machines (e.g., a pre-defined groupof machines in the datacenter) for deployment. For purely distributedrouters, such as the TLR 1205 as implemented in FIG. 12, the set ofphysical machines is not important, as the DR is implemented across themanaged forwarding elements that reside on hosts along with the datacompute nodes that connect to the logical network. However, if thelogical router implementation includes SRs, then these SRs will each bedeployed on specific physical machines.

In some embodiments, the user definition of a logical router includes aparticular number of uplinks. As described, an uplink is a northboundinterface of a logical router in the logical topology. For a TLR, itsuplinks connect to a PLR (all of the uplinks connect to the same PLR,generally). For a PLR, its uplinks connect to external routers. Someembodiments require all of the uplinks of a PLR to have the sameexternal router connectivity, while other embodiments allow the uplinksto connect to different sets of external routers. Once the user selectsa group of machines for the logical router, if SRs are required for thelogical router, the control plane assigns each of the uplinks of thelogical router to a physical machine in the selected group of machines(e.g., gateway machines). The control plane then creates an SR on eachof the machines to which an uplink is assigned. Some embodiments allowmultiple uplinks to be assigned to the same machine, in which case theSR on the machine has multiple northbound interfaces.

As mentioned above, in some embodiments the SR may be implemented as avirtual machine or other container, or as a VRF context (e.g., in thecase of DPDK-based SR implementations). In some embodiments, the choicefor the implementation of an SR may be based on the services chosen forthe logical router and which type of SR best provides those services.

In addition, the control plane of some embodiments creates the transitlogical switches. For each transit logical switch, the control planeassigns a unique VNI to the logical switch, creates a port on each SRand DR that connects to the transit logical switch, and allocates an IPaddress for any SRs and the DR that connect to the logical switch. Someembodiments require that the subnet assigned to each transit logicalswitch is unique within a logical L3 network topology having numerousTLRs (e.g., the network topology 1200), each of which may have its owntransit logical switch. That is, in FIG. 12, the transit logical switch1225 within the PLR implementation and the transit logical switch 1230between the PLR and the TLR1, each requires a unique subnet.

Some embodiments place various restrictions on the connection of logicalrouters in a multi-tier configuration. For instance, while someembodiments allow any number of tiers of logical routers (e.g., a PLRtier that connects to the external network, along with numerous tiers ofTLRs), other embodiments only allow a two-tier topology (one tier ofTLRs that connect to the PLR). In addition, some embodiments allow eachTLR to connect to only one PLR, and each logical switch created by auser (i.e., not a transit logical switch) is only allowed to connect toone PLR or one TLR. Some embodiments also add the restriction thatsouthbound ports of a logical router must each be in different subnets.Thus, two logical switches may not have the same subnet if connecting tothe same logical router. Lastly, some embodiments require that differentuplinks of a PLR must be present on different gateway machines. Itshould be understood that some embodiments include none of theserequirements, or may include various different combinations of therequirements.

The control plane of some embodiments generates a FIB for each routingcomponent of each logical router. FIG. 12 shows the FIBs 1250 and 1260for DRs (DR0 and DR1) that are generated based on the configuration dataand the RIBs of the PLR and TLR shown in FIG. 11. Each of these FIBsincludes the different routes implemented by the corresponding DR.Specifically FIB 1260 for DR1245 (DR1, generated DR of TLR1) includesthe same routes as were shown in RIB of TLR1. That is, FIB 1260 includesthe same three connected routes and on static routes of RIB 1160. Thisis because DR1 has inherited the same logical ports from the tenantlogical router 1110.

On the other hand, as shown in the figure, the generated FIB 1250 forthe DR 1205 has two connected routes, which connect DR0 1205 to thesubnet of transit logical switch 1230 as well as the subnet of transitlogical switch 1225. This FIB also includes three static routes two ofwhich are for the subnets of the two logical switch LS1 and LS2, whichare both via the northbound port of the DR 1245 (i.e., port D1), and onedefault route through the southbound port of the service router (i.e.,port SRP). In addition to configuring the FIBs of the DRs and SRs, thecontrol plane also assigns MAC addresses to the DR and SR interfaces insome embodiments.

Similar to DRs of a logical router, the control plane also configureseach SR of the logical router with a separate FIB and interfaces. Asdescribed above, SRs in some embodiments deliver services (i.e.,functionalities beyond simply routing, such as NAT, firewall, loadbalancing, etc.) and provide the connection between the logical networkand external physical networks. The configuration of the SRs inmulti-tier logical routers is done in the same manner that the SRs of asingle-tier logical router are configured. For example, as shown in FIG.12, since PLR 1105 has one uplink (U1), the control plane defines oneservice router (SR) 1210 for the PLR. This SR is assigned a southboundinterface, with an IP address of 192.168.100.1, which is in the samesubnet of the TLS 1225 (LS3), and a MAC address.

Similarly, for each southbound interface of a TLR, some embodiments adda route for the corresponding network to the RIB of each SR. This routepoints to the northbound DR interface of the TLR as the next-hop IPaddress of the southbound interface of the SR. Furthermore, any otherroutes configured for the logical router that egress from the southboundinterface are copied to the SR with the same northbound DR interface asthe next-hop IP address. On the other hand, a static route of thelogical router that egresses from an uplink (e.g., U1 or U2) is copiedto the FIB of the SR. In addition, the SRs of the PLR may learn dynamicroutes and place the learned dynamic routes in their FIB (though someembodiments perform this locally, without involving the centralizedcontrollers in the control plane).

As described above, the control plane of some embodiments generates andconfigures a set of forwarding tables on an MHFE (e.g., the TOR switch1140) using the OVSDB schema in order to logically connect the MHFE toone or more logical networks and also to enable the MHFE to performlogical routing functionalities on the L3 packets of these logicalnetworks. One of these tables is the tunnel endpoint locator table(Ucast_Macs_Remote table 1270 in OVSDB schema) that includes tunnelendpoint locations which specify the network layer (IP) addresses of theMFEs and MHFEs that implement the logical ports of logical switches towhich the machines (e.g., end machines, physical machines, etc.) and/orlogical ports of the logical routers are connected. By locating thetunnel endpoints, the MFEs and MHFEs are able to establish tunnelsbetween themselves and exchange the logical network data through theestablished tunnels (VXLAN tunnels).

As shown in FIG. 12, the tunnel endpoint locator (Ucast_Macs_Remote)table 1270 that is generated on the TOR switch 1140 (e.g., by the OVSDBschema) has several different fields. These fields, as described for thetunnel endpoint locator table 540 of FIG. 5, include (i) a logicalswitch field that species the logical switch to which a port of amachine or a logical router is connected, (ii) a MAC address field thatspecifies the corresponding MAC address of the port, and (iii) a locatorfield that specifies the IP address of the tunnel endpoint for thecorresponding MAC address.

Also as described above, when the MHFE (e.g., the hardware VTEP)realizes that the destination MAC address of a packet belongs to a portof the distributed routing component, the VTEP does not establish atunnel for routing the packet because the distributed routing componentis implemented by every single MFE, MHFE, and gateway that participatesin the logical network. As such, a packet with a destination MAC addressof the logical router is not required to be routed to any other node inthe network. However, some embodiments populate the tunnel endpointlocator table with the tunnel endpoint data of each logical port of theservice routing components that is connected to a logical forwardingelement (e.g., an L2 logical switch).

That is, for each logical port of the SRs, some embodiments store (i) inthe logical switch field, the logical switch to which the port isconnected (e.g., the transit logical switch to which the southbound portof the service component is connected), (ii) in the MAC address field,the MAC address of the port, and (iii) in the locator field, the IPaddress of the tunnel endpoint that implements the logical switch portto which the service component port is connected (e.g., the IP addressof the gateway machine that implements the service routing component).

For example, for the MAC address of the logical port L1 of the DR1(MAC-L1) which is connected to the logical switch LS1, the control planestores 127.0.0.1 (localhost) as the IP address of the tunnel endpointlocator field. Similarly, the MAC addresses MAC-L2, MAC-DRP, MAC-D1, andMAC-D2, which are the MAC addresses of the other ports of thedistributed routers DR0 and DR1, and are connected to the logicalswitches LS2, L3, and LS4 also have the same loopback IP address of127.0.0.1 (localhost) stored in their corresponding tunnel endpointlocator field.

For the service components of the logical router, however, the controlplane stores the IP addresses of the gateway machines that implement(e.g., through the MFEs that the gateway machines execute) the logicalswitch ports that are connected to the SR ports. That is, the SR portSRP with the MAC address MAC-SRP is implemented by the gateway machineGateway1 (not shown in the figure). As such, the control plane stores,in the locator field, the IP address of Gateway1.

FIG. 13 illustrates the configuration data propagated in differentdatabase tables stored on an MHFE using the OVSDB schema in order toenable the MHFE to infer the data link layer (MAC) address of logicalports of multi-tier logical routers. The MHFE for which the tables areillustrated is the TOR switch 1140 shown in FIG. 12. As shown in thefigure the logical router table 1210 (Logical_Router table) is a tablethat is configured to map the IP addresses of logical ports of a logicalrouter to one or more logical switches. Since a logical router isdivided to separate distributed and service routers in some embodiments,the control plane of some embodiments configures each of these routingcomponents as a separate router in this table. As illustrated, thelogical router table includes an ID field that identifies the router, aswitch binding field that maps the different IP addresses of thedifferent ports of the router to a logical switch, and a static routefield that specifies the different static routes included by the router.

As shown, the table 1310 includes a DR row (with DR1/DR2 in ID field)for each of the distributed routers 1205 and 1245 of FIG. 12, and one SRrow for the service router 1210. The corresponding switch binding fieldfor DR1 has the IP address of logical port L1 (1.1.1.253/24) which ismapped to the logical switch 1125 (LS1); the IP address of logical portL2 (1.1.2.253/24) is mapped to the logical switch 1130 (LS2); and the IPaddress of logical port D1 (2.0.0.1/31) which is mapped to the transitlogical switch 1230 (LS4). The remaining routes specified in the FIB1260 are the static routes. In other words, the connected routes of theFIB 1260 of the routing component DR1 form the switch-binding field ofthe routing component DR1, and the remaining routes in the FIB 1310 formthe static routes field in some embodiments. Therefore, the staticroutes field of the table 1310 shows the only remaining route (i.e., thedefault route) in the static routes field for DR1.

The corresponding switch binding field for DR0 has the two connectedroutes of the FIB 1250 which are the IP address of logical port D2 thatis mapped to the logical switch LS4 and the IP address of logical portDRP, which is mapped to the logical switch LS3. The remaining routes ofthe FIB 1250 will be the static routes for DR0. Therefore, the staticroutes field of the table 1310 shows the three remaining route in thestatic routes field for DR0 in the static routes field of this router.These routes include the default route, which is reached via thesouthbound interface of the SR (SRP port). The subnets of the first andsecond logical switches (LS1 and LS2) are reached through the northboundinterface (D1 port) of the DR 1245 (DR1).

The table 1310 also shows that the switch-binding field for the servicerouting component SR maps the IP address of the southbound logical portSRP (192.168.100.1/30) to the logical switch LS3. In some embodiments,when there is no logical switch associated with the northbound logicalports of the service routers (e.g., when the uplinks of the router areconnected directly to a physical router that connects the router to anexternal network), no switch binding field for those logical ports arepopulated in the logical router table. Finally, the static route for theservice router is the remaining route of the FIB of this router whichshows, e.g., an IP address of the next hop physical router towards theexternal network.

The illustrated table 1320 is the same as the table 1270 shown in FIG.12 with the exception that this table now shows an additional optionalfield for holding a corresponding IP address for each MAC addresspopulated in the MAC address field (i.e., the MAC field in theUcast_Macs_Addresses table) in the OVSDB schema. As described above, thecontrol plane of some embodiments populates the IP address of eachlogical port of the routing components in this field in order to (1)link the Ucast_Macs_Addresses table 1320 to the Logical_Router table1310 and (2) enable the TOR switch 1140 to infer the MAC addresses ofthe logical router ports and thereby identify the packets that aredestined for the logical router implemented by the TOR switch 1140.

As an example, when the TOR switch receives a packet that has adestination MAC address MAC-D1 in the data link layer of the packetheader, the TOR switch of some embodiments retrieves the correspondingIP address for this MAC address (i.e., IP address IP-D1) from the tunnellocator table 1320 and matches this IP address against the IP addressesof the logical router table 1310. The TOR switch then realizes that theMAC address belongs to one of the ports of the distributed router DR1that is associated with the logical switch LS4. As such, the TOR switchconcludes that the packet is an L3 packet and starts L3 processing onthe packet (e.g., in the same manner for packet processing described byreference to the examples of FIG. 9 above).

In some other embodiments, as described above, the control plane tagsthe MAC addresses of the logical ports of a logical router during theconfiguration of the tunnel endpoint locator table. The control planetags these MAC addresses by populating a corresponding IP address foreach MAC address of the table and linking the corresponding IP addressesto the IP addresses of logical ports of the logical router populated inthe logical router table. In some such embodiments, the TOR switchsimply looks up the MAC address of the received packet in the tunnelendpoint locator table 1320 and starts L3 processing on the packet whenthe MAC address of the packet matches one of the tagged MAC addresses inthe table.

While the SR setups in the above-described sections are foractive-active configuration (using ECMP), some embodiments use anactive-standby configuration with two SRs. Some embodiments use theactive-standby configuration when stateful services are configured onthe SRs. In this case, the benefit of avoiding having to continuouslyshared state between the SRs may outweigh the negatives of sending allof the northbound and southbound traffic between multiple SRs (whileusing a standby for backup in case of failure). In the active-standbymode, the state is periodically synchronized between the two SRs (i.e.,between the active and standby SRs), though this need not be done forevery packet.

In some embodiments, for active-standby configuration, the administratoris required to configure two uplinks when defining the logical router,and the uplinks need not be in the same L2 domain. However, because theactive and standby SRs should be equivalent options to the DR (with theactive SR the preferred of the two options), some embodiments requirethe two SRs to have uniform L3 connectivity. This is, of course, not anissue when the active-standby SRs are configured for a TLR with statefulservices, as both SRs will have one next hop, the DR of the PLR to whichthe TLR connects. For a PLR in active-standby configuration, the twouplinks are configured with the same connectivity in some embodiments.For a PLR, some embodiments allow (or require) performing dynamicrouting protocols (e.g., BGP) on the SRs.

FIG. 14 illustrates a logical network topology 1400 that includessingle-tier logical router and a RIB that defines the routes of thelogical router. The network topology 1400 is similar to that of FIG. 4,with the exception that this figure shows only one L3 connectivity forthe uplink of a logical router. The logical network topology 1400includes two logical switches 1405 and 1410 that are connected to alogical router 1415. The configuration of these components is the sameas with the network topology 400, except for the configuration of theuplinks and the physical routers to which the uplinks connect.

That is, there is only one uplink interface that connects the logicalnetwork to an external network 1425 through the physical router 1420 andfor this uplink, the user (e.g., network administrator) has definedstateful services (e.g., NAT, load balancing, etc.) and has associatedthe uplink port (i.e., port U1) with two different edge nodes (e.g.,gateway machines). The user of some embodiments is able to associate oneuplink of a logical router to more than one edge node through a set ofAPIs. As a result of configuring the uplink on two edge nodes, thecontrol plane, as shown below in FIG. 15, configures (defines) twodifferent service routers, one of which would be an active servicerouter while the other one would operate as a standby service router.

As shown, the logical switches 1405 and 1410 are each assigned its ownsubnet (1.1.1.0/24 and 1.1.2.0/24), and all of the data compute nodesand MHFEs attached to the logical switches 1405 and 1410 will have IPaddresses in the corresponding subnet. The logical router 1415 has aninterface L1 to the first logical switch 1405, with an IP address of1.1.1.253 that is the default gateway for the data compute nodes andMHFEs in the subnet 1.1.1.0/24, including the VM 1440. The logicalrouter 1415 also has a second interface L2 to the second logical switch1410, with an IP address of 1.1.2.253 which is the default gateway forthe data compute nodes and MHFEs in the subnet 1.1.2.0/24, including theTOR switch 1450.

The northbound side of the logical router 1415 has an uplink U1, whichhas an IP address of 192.168.1.253 and connects to the physical router1420 with an IP address of 192.168.1.252. The physical router 1420 isnot actually a part of the logical network 1400, but rather connect thelogical network to the external network 1425. Although not shown, eachof the logical ports of the logical router is also assigned a separatedata link layer (MAC) address.

Based on these example addresses, the RIB 1460 defines the differentroutings performed by the router 1415. Specifically, the RIB includesthree connected routes based on the subnets configured on the southboundand northbound interfaces of the logical router. These three connectedroutes include a route that egresses from logical port L1 for any packetthat has a destination IP address that is in the subnet of LS1; a routethat egresses from the logical port L2 for packets with destination IPaddresses that belong to the subnet of LS2; and a route that egressesthe logical port U1 for packets with destination IP addresses thatbelong to the subnet of U1 and/or physical router 1420. The RIB 1460also includes one other static route through the physical router 1420,which is a default route for other packets.

FIG. 15 illustrates a control plane view 1500 of the logical networktopology 1400 of FIG. 14 when the logical router is configured inactive-standby mode, rather than active-active (ECMP) mode.Specifically, the logical router 1415 includes two SRs 1510 and 1515,one of which is an active SR while the other is an standby SR (i.e., instandby for the active SR). The control plane configures the DR 1505 inthe same manner as in the general case of FIG. 5, in terms of assigningMAC and IP addresses to its southbound and northbound interfaces. Whenconstructing the FIB 1530, the same connected routes are used, and thesame static route rules apply. The only important difference betweenthis figure and the active-active SR mode shown in FIG. 5 is thatbecause the logical router provides stateful services, the single uplinkport is configured on two different edge nodes. As such, the southboundinterfaces of the SRs 1510 and 1515 are assigned the same IP address(i.e., IP address 192.168.100.1). These two southbound ports of the SRs1510 and 1515 will be assigned different MAC addresses though.

Each of the SRs 1510 and 1515 will be configured in mostly the samemanner. When the logical router 1415 is a PLR (or in a one-tiertopology, as in the example), the IP and MAC addresses of the northboundinterfaces are the same as those assigned to the uplinks configured forthe PLR. On the other hand, when the logical router 1415 is a TLR, itmay only have one uplink that is configured to connect to the PLR. Inthis case, the IP addresses of the two northbound interfaces are thesame, but each SR is assigned a different MAC address. Similarly, ineither of these two cases (PLR or TLR), a single IP address is assignedto the two southbound interfaces, with two different MAC addresses forthe two SRs.

Any uplink-independent service policies are pushed by the controller (inthe control plane) to both of the SRs identically, in some embodiments.If any service policies that depend on the uplink are allowed andconfigured, then these are pushed to the SRs on which the uplink withwhich they are associated exists. In addition, any dynamic routingconfigurations of a logical router port are transferred to thenorthbound interface of the SRs.

The FIB 1550 for the SRs 1510 and 1515 is similar to that describedabove for the general case. Static and connected routes that egress froman uplink of the logical router are added to the FIB 1550 of the SRswithout modification. For each southbound interface of the logicalrouter (e.g., routes for logical switch subnets), a route for thenetwork is added with the next hop IP address set to the northboundinterface of the DR. The FIB 1550 for the SRs 1510 and 1515, as shown inthe example of FIG. 15 will include the following routes, prior tolearning any additional routes via dynamic routing protocols: anydefault route 0.0.0.0/0 should be output to U1 via 192.168.1.252 (i.e.,the IP address of physical router 1420); any IP address in the subnet192.168.1.0/24 (subnet of port U1) should be output to U1. Any IPaddress in the subnets of LS1 and/or LS2 should be routed via northboundport of the DR (i.e., port DRP with IP address of 192.168.100.0).

As mentioned, the SRs 1510 and 1515 are in active-standby mode. In someembodiments, when a SR is set as a standby SR (rather than active SR),the SR does not answer to the ARP requests on its southbound interfacein some embodiments. ARP packets for the southbound IP of the SR will bebroadcast on the transit logical switch that connects the SRs and theDR, and both the active and standby SRs will be responsive to that IPaddress. However, only the active SR will respond to ARP requests, sothat the DR will route packets to the MAC address of the active SRrather than the standby SR. The standby SR in some embodiments willnevertheless accept packets received by the northbound interface, inorder to run its dynamic routing protocol and keep an up-to-date set ofroutes in case it becomes the active SR. However, the standby SR doesnot advertise prefixes to the external networks, unless it becomesactive.

In some embodiments, the gateway machines (not illustrated) thatimplement the active SR and the standby SR (SRs 1510 and 1515) monitoreach other's liveness over a tunnel between them in some embodiments. Incase the active SR fails, the standby SR takes over its responsibilitiesand the active SR becomes the standby SR. The failure may occur due tothe machine on which the SR operates crashing completely, the datacompute node or datapath software that implements the machinecorrupting, the ability of the SR to connect to either the externalnetwork or through tunnels to other components of the logical networkfailing, etc. On the other hand, when a standby SR fails someembodiments take no action.

As shown in FIG. 15, the generated FIB 1530 for the DR 1505 has threeconnected routes, which connect (i) the logical port L1 to the subnet ofthe logical switch LS1, (ii) the logical port L2 to the subnet of thelogical switch LS2, and (iii) the logical port DRP to the subnet oftransit logical switch 1520. The FIB 1530 also includes a static route,which is the default route through the IP address that is shared betweenthe active and standby SRs 1510 and 1515 for their southbound ports(i.e., 192.168.100.1 shared by the ports SRP1 and SRP2).

As shown in the figure, the tunnel endpoint locator (Ucast_Macs_Remote)table 1540 is configured on the TOR switch 1450 (e.g., through the OVSDBschema) to have a tunnel locator address of 127.0.0.1 (localhost) foreach MAC address of the logical ports of the DR 1505 (i.e., MAC-L1,MAC-L2, and MAC-DRP), since DR 1505 is implemented on all of the managedhardware and software forwarding elements that implement the logicalswitches and routers of the logical network.

For the service components of the logical router 1415, however, thecontrol plane stores the IP addresses of the gateway machines thatimplement (through the MFEs that the gateway machines execute) thelogical switch ports that are connected to the SR ports. That is, the SRport SRP1 with the MAC address MAC-SRP1 is implemented by the gatewaymachine GW1 (not shown in the figure). As such, the control planestores, in the locator field, the IP address of GW1, while the SR portSRP2 with the MAC address MAC-SRP2 is implemented by the gateway machineGW2 (not shown in the figure either) and therefore, the control planestores the IP address of GW2 in the locator field.

FIG. 16 illustrates the configuration data propagated in differentdatabase tables 1610 and 1620 stored on an MHFE using the OVSDB schemain order to enable the MHFE to infer the MAC address of logical ports ofthe logical router. The MHFE for which the tables are illustrated is theTOR switch 1450 shown in FIG. 15. As shown in the figure, the logicalrouter table 1610 (Logical Router table) includes a row for thedistributed router 1505 (DR row) and rows for the service routers 1510and 1515 (SR1 row and SR2 row). The corresponding switch-binding fieldof the DR row includes: the IP address of logical port L1(1.1.1.253/24), which is mapped to the logical switch LS1; the IPaddress of logical port L2 (1.1.2.253/24), which is mapped to thelogical switch LS2; and the IP address of logical port DRP(192.168.100.0), which is mapped to the transit logical switch (LS3).The only static route populating the static routes field for the DR isthe default route through the share IP address of the southboundinterfaces of SR1 and SR2.

The table 1610 also shows that the switch-binding field for the servicerouting components SR1 and SR2 maps the shared IP address192.168.100.1/30 of the southbound logical ports SRP1 and SRP2 to thelogical switch LS3. Finally, the static route for each of the SRs(active and standby) is the remaining route of the FIB of this routers,which shows an IP address 192.168.1.252 of the next hop physical routertowards the external network (in this case, the next hop address forboth of the SRs is the same).

The illustrated table 1620 is the same table 1540 shown in FIG. 15 withthe exception that the table 1620 shows an additional optional IPaddress field for holding a corresponding IP address for each MACaddress populated in the MAC address field (i.e., the MAC field in theUcast_Macs_Addresses table) in the OVSDB schema. As described above, thecontrol plane of some embodiments populates the IP address of eachlogical port of the routing components in the optional IP address fieldin order to (1) link the table 1620 (i.e., Ucast_Macs_Addresses table)to the table 1610 (Logical_Router table) and (2) enable the TOR switch1450 to infer the MAC addresses of the logical router ports and therebyidentify the packets that are destined for the logical routerimplemented by the TOR switch 1450.

Additionally, as shown in the figure, the IP address for southboundports of the SRs are not configured by the control plane in the optionalIP address field of the table 1620 (e.g., for either MAC-SRP1 orMAC-SRP2). This is due to the active-standby nature of the servicerouters (SR1 1510 and SR2 1515). In some embodiments, when the controlplane configures the tunnel endpoint locator table (i.e.,Ucast_Macs_Remote table), the control plane does not populate theoptional IP address fields of this table for any service routingcomponent of the logical router that operates in active-standby mode(e.g., when the logical router 1415 provides stateful services).

In some such embodiments, the control plane leaves the task ofidentifying the corresponding IP address of each MAC address of the SR'ssouthbound ports for the hardware VTEP (MHFE) to perform. In someembodiments, the hardware VTEP must resolve this IP address when needed,in which case the active SR on the corresponding edge node would respondwith the MAC address of the active SR (e.g., MAC-SRP1 or MAC-SRP2).

As an example, when the TOR switch receives a packet that has adestination MAC address MAC-DRP in the data link layer of the packetheader, the TOR switch of some embodiments retrieves the correspondingIP address for this MAC address (i.e., IP address IP-DRP) from thetunnel locator table 1620 and matches this IP address against the IPaddresses of the logical router table 1610. The TOR switch then realizesthat the MAC address belongs to one of the ports of the distributedrouter 1505 that is associated with the transit logical switch LS3. Assuch, the TOR switch concludes that the packet is an L3 packet andstarts L3 processing on the packet (e.g., in the same manner describedabove for packet processing by reference to the examples of FIG. 9).

In some other embodiments, as described above, the control plane tagsthe MAC addresses of the logical ports of a logical router during theconfiguration of the tunnel endpoint locator table. The control planetags these MAC addresses by populating a corresponding IP address foreach MAC address of the table and linking the corresponding IP addressesto the IP addresses of logical ports of the logical router populated inthe logical router table. In some such embodiments, the TOR switchsimply looks up the MAC address of the received packet in the tunnelendpoint locator table 1620 and starts L3 processing on the packet whenthe MAC address of the packet matches one of the tagged MAC addresses inthe table

IV. Configuring MHFE as an Edge Node

The above sections described implementation of the service routingcomponents (SRs) on one or more gateway machines to connect a logicalnetwork to one or more external physical networks. As described above,the gateway machines, in some embodiments, are host machines that hostservice routers rather than user VMs. Additionally, each of the gatewaymachine of some embodiments includes an MFE that implements the logicalforwarding elements of a logical network (e.g., L2 switches, DR, etc.)in a manner similar to the other MFEs operating on other host machinesof a datacenter. In some embodiments the SRs are separate from the MFEsthat operate on the gateway machines, while in other embodiments, SRsare implemented by the MFEs of the gateway machines in a similar mannerthat the other logical forwarding elements are implemented.

Instead of configuring a SR on a gateway machine, some embodimentsconfigure a service routing component of a logical router on an edgehardware VTEP (i.e., an edge MHFE) in order to connect a logical networkto external physical networks through the edge hardware VTEP. In otherwords, some embodiments configure an edge MHFE to enable the MHFE to actas a gateway machine to communicate with the external networks.

When a user (e.g., a datacenter administrator) wishes to configure anedge MHFE (e.g., a third-party managed hardware switch) as the gatewayof a logical network (e.g., a tenant logical network), the user attachthe uplink port (i.e., the northbound interface of the logical routerthat communicates with external routers) of the logical router to theedge MHFE when defining the logical router. In other words, the userdefines the MAC and IP addresses of the uplink port to be bound to oneof the physical ports of the MHFE (e.g., a physical port of a TORswitch).

When the control plane receives the definition of a logical router, inwhich, the uplink port is defined to be attached to a physical port ofan MHFE (i.e., the physical port is assigned the same IP and MACaddresses of the uplink port), the management plane instantiates boththe distributed component and service components of the logical routeron the MHFE. That is, the management plane configures the MHFE (e.g.,through the OVSDB schema) to not only implement the DR of the logicalrouter but to implement the SR(s) of the logical router as well. Inorder to bind the uplink port of the logical router to the physical portof the MHFE, in some embodiments, the management plane defines a newuplink logical switch (ULS) for handling the communications between theSRs implemented on the MHFE and the external networks. In someembodiments the defined uplink logical switch is hidden from the userthat configures the logical router through the API, with the possibleexception of inspection and troubleshooting purposes.

In some embodiments, the control plane defines the southbound interfaceof the uplink logical switch (ULS) to be associated with the physicalport of the edge MHFE having the MAC and IP addresses of the uplink portof the logical router. In some such embodiments, the management planedefines the northbound interface of the ULS to be associated with anexternal network (e.g., a southbound port of a next hop physical routerthat connects the logical network to one or more external networks).

Additionally, the ULS is associated with the uplink port of the logicalrouter and therefore it does not participate in any tunneling mesh. Thatis, since the edge MHFE is the only logical network element thatimplements the ULS in the physical network, the MHFE does not establishany tunnel (e.g., VXLAN tunnel) to any other managed forwarding element(e.g., an MFE, an MHFE, etc.) and/or gateway machine that implements alogical switch.

FIG. 17 illustrates a control plane view and physical realization of alogical network topology, in which an edge MHFE implements the servicecomponent of the logical router and communicates with external networksthrough the service component. Specifically this figure illustrates acontrol plane view 1700 of the logical network topology 1400 of FIG. 14and a physical realization 1701 of this logical network topology. Thecontrol plane view illustrates a logical router 1760 that is configured(by the control plane) to have a DR 1765 that is the southboundinterface of the logical router (connected to logical switches LS1 andLS2), and a SR that is the northbound interface of the logical router(connected to the next hop physical router 1750).

The control plane view also shows that the physical port A on TOR switch1740 is logically connected to the logical network through the logicalswitch LS1, while port B of VM1 (that is physically implemented by theMFE 1780 running on the host machine 1775) is logically connected to thelogical network through the logical switch LS2.

The physical realization shows a host machine 1775, a TOR switch 1740,and an edge TOR 1710. The host machine 1775 executes the virtual machineVM1 and the MFE 1780. The MFE 1780 implements the different logicalswitches of the logical network (i.e., LS1 and LS2) as well as the DRand TLS of the logical router 1760. The TOR switch 1740 has severalservers (e.g., third-party servers) Server1-Server(n) connected to itsports and as such connects these servers to the logical router 1760 andthe logical switches LS1 and LS2 by implementing the DR 1765 of thelogical router 1760 and the logical switches LS1 and LS2, respectively.

In this example, the user has attached, in the definition of the logicalrouter, the uplink interface of the logical router to the edge TORswitch 1710. That is, when the control plane receives the userdefinition of the logical router 1760, the control plane realizes thatthe MAC and IP addresses of the uplink port of the logical router (portU1) are assigned to one of the physical ports of the edge TOR switch1710. As such, the control plane of some embodiments configures the edgeTOR switch 1710 to implement the SR of the logical switch (asillustrated in the OVSDB tables below by reference to FIG. 18).

The control plane also defines a new uplink logical switch 1720. Thesouthbound port of the ULS 1720 is defined to be associated with thephysical port of the edge TOR switch 1710 that is bound to the uplinkport of the logical router. As shown, the southbound port of the ULS isassociated with the physical port of the TOR switch, which has the IPaddress of port U1 (192.168.1.253), while the northbound port of the ULSis associated with the southbound port of the physical router 1750 whichhas the IP address of 192.168.1.252. In this manner, and as describedbelow in the provided packet processing example, any logical network L3packet that is to be sent to a machine in an external network will besent out of the logical network through the physical port of the edgeTOR switch 1710 that is associated with the southbound port of the ULS1720.

Although the uplink logical switch 1720 is illustrated as a separatenetwork element in the physical realization of the logical networktopology, it should be understood that this ULS 1720 is implemented bythe edge TOR switch 1710 similar to the TLS 1775, SR 1770, and DR 1765of the logical router 1760. It is not a separate network element in thephysical implementation. The ULS logical switch 1720 is only shown as aseparate element to demonstrate the connection of TOR switch 1740 withthe external network.

It is also important to note that although the edge TOR switch 1710shown in the figure is a separate TOR switch from the TOR switch 1740that logically connects the physical servers to the logical network,some embodiments configure the same TOR switch 1740 to act as thegateway of the logical network as well. That is, when a user defines thelogical router in such a way that the uplink port of the logical routeris mapped to a physical port of the TOR switch 1740, the control planeof some embodiments configures the SR of the logical router to beimplemented by the TOR switch 1740.

The control plane also defines a new ULS that connects the mapped portof the TOR switch to the external networks in the same manner that isdescribed above. Therefore for the same TOR switch, a first set ofphysical ports are logically connected to a logical network to connect aset of physical machines and devices to the logical network, while asecond set of physical ports are connected to one or more externalnetworks. This way, a single TOR switch is able to connect all themachines of one or more logical networks to one or more externalnetworks.

It should also be understood that even though in all of the examplesprovided above and below, the MHFE is logically connected to one logicalnetwork, an MHFE may logically connect to many more logical networks (ofmany other tenants of a datacenter) at the same time. In someembodiments, an MHFE can connect to one logical network through one setof physical ports while it can connect to a second logical networkthrough a second set of physical ports.

FIG. 18 illustrates an example of the configuration data propagated indifferent database tables stored on the edge MHFE of FIG. 17, using theOVSDB schema. Specifically, this figure shows a logical router table1810 (Logical_Router table) and a tunnel endpoint locator table 1820(Ucast_Macs_Remote).

The logical router table 1810 (Logical Router table) includes a DR rowfor the distributed router 1765 and an SR row for the service router1770. The corresponding switch binding field for the DR has the IPaddress of logical port L1 (1.1.1.253/24) which is mapped to the logicalswitch LS1; the IP address of logical port L2 (1.1.2.253/24) which ismapped to the logical switch LS2; and the IP address of logical port DRP(192.168.100.3) which is mapped to the transit logical switch (LS3). Theonly static route populated in the static routes field for the DR is thedefault route which is through the IP address of the southboundinterface SRP (192.168.100.1) of the SR 1770.

The logical router table 1810 also shows that the switch-binding fieldfor the service routing component SR maps two IP addresses to twodifferent logical switches. This is because unlike the previousexamples, the northbound port of the SR is also associated with alogical port of a logical switch (i.e., ULS). Therefore, the IP addressof the southbound logical port SRP (192.168.100.1/30) is mapped to thetransit logical switch LS3, while the IP address of the northboundlogical port U1 (192.168.1.253) is mapped to the uplink logical switchULS. Finally, the static routes for the service router is the remainingroutes of the FIB of the SR. As shown, the static routes include, adefault route which is through the IP address of the southboundinterface of the physical router 1750 (192.168.1.253), and any packetwith the destination subnet address of LS1 and/or LS2 should be routedthrough the northbound interface of the DR (i.e., port DRP with IPaddress of 192.168.100.0).

The tunnel endpoint locator table 1820 shows how the control plane haspopulated the different fields in the OVSDB schema in order to configureboth TOR switch 1740 and edge TOR switch 1710. As described above, thecontrol plane of some embodiments populates the IP address of eachlogical port of the routing components in this field in order to (1)link the table 1820 (i.e., Ucast_Macs_Addresses table) to the table 1810(Logical_Router table) and (2) enable the TOR switches 1710 and 1740 toinfer the MAC addresses of the logical router ports and thereby identifythe packets that are destined for the logical router implemented by theTOR switch.

As shown in the table 1820, the MAC address of port A (MAC-A) of the TORswitch 1740 (of FIG. 17) is associated with a logical port of thelogical switch LS1 and has a corresponding IP address of IP-A. Thetunnel endpoint locator for the logical switch LS1 indicates that theTOR switch 1740 is implementing this logical switch for this port MACaddress (MAC-A). Additionally, the MAC address of southbound port of theSR (MAC-SRP) is associated with a logical port of the transit logicalswitch LS3 and has a corresponding IP address of IP-SRP. Unlike all ofthe previous examples in which the transit logical switch associatedwith the SR port was implemented on a gateway machine, the SR in thisexample is implemented on the edge TOR switch 1710. The tunnel endpointlocator for the logical switch LS3 indicates that TOR switch 1710 isimplementing the logical switch for this port MAC address (MAC-SRP).

Furthermore, as described above, the newly defined uplink logical switch1720 (ULS) for the uplink port of the logical router is not a VXLANbacked logical switch. In other words, this logical switch (ULS) doesnot participate in the mesh of overlay tunnels between the managedforwarding elements (e.g., MFEs and MHFEs) that implement the logicalswitches. As such, the locator field of the table 1820 for the MACaddress of port U1 that is associated with the logical switch ULS ispropagated (by the control plane) with the fixed loopback address127.0.0.1 (localhost). As described before, this address indicates thatno tunnel should be established to any other managed forwarding elementfor logical switch 1720.

As an example, when the TOR switch receives a packet that has adestination MAC address MAC-SRP in the data link layer of the packetheader, the TOR switch of some embodiments retrieves the correspondingIP address for this MAC address (i.e., IP address IP-SRP) from thetunnel endpoint locator table 1820 and matches this IP address againstthe IP addresses of the logical router table 1810. The TOR switch thenrealizes that the MAC address belongs to one of the ports of the SR thatis associated with the transit logical switch LS3. As such, the TORswitch concludes that the packet is an L3 packet and starts L3processing on the packet.

In some other embodiments, as described above, the control plane tagsthe MAC addresses of the logical ports of a logical router during theconfiguration of the tunnel endpoint locator table. The control planetags these MAC addresses by populating a corresponding IP address foreach MAC address of the table and linking the corresponding IP addressesto the IP addresses of logical ports of the logical router populated inthe logical router table. In some such embodiments, the TOR switchsimply looks up the MAC address of the received packet in the tunnelendpoint locator table 1820 and starts L3 processing on the packet whenthe MAC address of the packet matches one of the tagged MAC addresses inthe table.

An example packet processing which involves north-south routing is nowdescribed. In the example, the physical machine is connected to port Aof the hardware VTEP that is associated with the logical switch LS1 asshown in FIG. 17, and has an IP address of IP-A (1.1.1.1) and a MACaddress of MAC-A. Also the virtual machine VM has a virtual interface(port B) which is implemented on MFE 1780. In the provided example thephysical machine on port A, sends a packet to a machine connected to anexternal network with an IP address of 10.10.10.10.

The default gateway for the TOR switch 1740 is the L1 port of the DR1765 (the default gateway has been assigned to the TOR switch byassigning a static IP address to its different ports including port B,or through a DHCP service). The default gateway port L1 is in the samesubnet as port A and has an IP address of 1.1.1.253 and a MAC address ofMAC-L1 as shown in the FIG. 17. Therefore, the physical machine (e.g. aserver connected to port A of the TOR switch) sends an L3 packet thathas a destination MAC address of MAC-L1, a source MAC address of MAC-A,a destination IP address of 10.10.10.10 (i.e. the IP address of externalmachine connected to the external network), and a source IP address ofIP-A.

It should be noticed that the MAC address of the default gateway portcan be learned by sending an ARP request from the physical machine(e.g., server) connected to port A to the hardware VTEP, which inresponse yields the MAC address using the Ucast_Macs_Remote table (sincethe hardware VTEP knows that port A is associated with the logicalswitch LS1 and therefore the MAC address associated with this logicalswitch in the table is MAC-L1).

After the L3 packet is received at the TOR switch 1740, the TOR switchrealizes that the packet is an L3 packet because the destination MACaddress of the packet is MAC-L1, which is a MAC address of one of theports of the logical router. As such, the TOR switch performs L3processing on the packet. The TOR switch starts to perform the L3processing by replacing the destination MAC address of the packet(MAC-L1) with the destination MAC address of the SRP port of SR 1770associated with one of the logical ports of the transit logical switchLS3. The TOR switch also replaces the source MAC address MAC-A with theMAC address of northbound logical port of the DR 1765. The source anddestination IP addresses remain the same.

In order to replace the source MAC address, the TOR switch 1740 looks atthe static route column of the logical router table 1810 (shown in FIG.18) and based on the destination IP address of the packet (i.e.,10.10.10.10) determines that the packet should be sent from the egressport of the DR to the default port SRP (192.168.100.1) of the SR 1770.The TOR switch also looks up the destination IP address in the tunnellocator table 1820 and the matched record in this table yields thesouthbound logical port of the SR as well as the tunnel endpoint locatoraddress of the edge TOR switch 1710 that implements the transit logicalswitch LS3 associated with this port (port SRP). The TOR switch thenestablishes a VXLAN tunnel to the identified tunnel endpoint (TOR switch1710) and sends the packet to the destination port using the VXLANtunnel (e.g., after adding the tunnel encapsulation data to the packet).

When the packet arrives at the edge TOR switch 1710, the edge TOR switchfrom the tunnel endpoint locator table 1820 for MAC-SRP, and the logicalrouter table for SR, infers that the destination MAC address of thepacket belongs to a logical router port and as such the packet is an L3packet. Hence, the edge TOR switch 1710 starts to run logical routerfunctionalities on the packet. Based on the static routes of the logicalrouter table, the edge TOR switch realizes that the packet needs to berouted to the next hop physical router 1750 (192.168.1.252) from theuplink port U1 (192.168.1.253). These two IP addresses are associatedwith the uplink logical switch 1720 (ULS).

If needed, the edge TOR switch would perform an ARP request for the IPaddress of the physical router (192.168.1.252) from port U1 (using IP-U1as source IP, and MAC-ill as source MAC, which are provided in the table1820). Once, the ARP request is resolved, the edge TOR switch would havethe MAC address of the southbound port of the physical router 1750. Assuch, the edge TOR switch 1710 replaces the destination MAC address withthe MAC address of the physical router port that has the correspondingIP address 192.168.1.252. The edge TOR switch also replaces the sourceMAC address with the MAC address of the uplink port U1 (MAC-U1) andsends the packet to the next hop physical router through the physicalport on which the MAC address MAC-ill is mapped.

V. Electronic System

Many of the above-described features and applications are implemented assoftware processes that are specified as a set of instructions recordedon a computer readable storage medium (also referred to as computerreadable medium). When these instructions are executed by one or moreprocessing unit(s) (e.g., one or more processors, cores of processors,or other processing units), they cause the processing unit(s) to performthe actions indicated in the instructions. Examples of computer readablemedia include, but are not limited to, CD-ROMs, flash drives, RAM chips,hard drives, EPROMs, etc. The computer readable media does not includecarrier waves and electronic signals passing wirelessly or over wiredconnections.

In this specification, the term “software” is meant to include firmwareresiding in read-only memory or applications stored in magnetic storage,which can be read into memory for processing by a processor. Also, insome embodiments, multiple software inventions can be implemented assub-parts of a larger program while remaining distinct softwareinventions. In some embodiments, multiple software inventions can alsobe implemented as separate programs. Finally, any combination ofseparate programs that together implement a software invention describedhere is within the scope of the invention. In some embodiments, thesoftware programs, when installed to operate on one or more electronicsystems, define one or more specific machine implementations thatexecute and perform the operations of the software programs.

FIG. 19 conceptually illustrates an electronic system 1900 with whichsome embodiments of the invention are implemented. The electronic system1900 may be a computer (e.g., a desktop computer, personal computer,tablet computer, etc.), server, dedicated switch, phone, PDA, or anyother sort of electronic or computing device. Such an electronic systemincludes various types of computer readable media and interfaces forvarious other types of computer readable media. Electronic system 1900includes a bus 1905, processing unit(s) 1910, a system memory 1925, aread-only memory 1930, a permanent storage device 1935, input devices1940, and output devices 1945.

The bus 1905 collectively represents all system, peripheral, and chipsetbuses that communicatively connect the numerous internal devices of theelectronic system 1900. For instance, the bus 1905 communicativelyconnects the processing unit(s) 1910 with the read-only memory 1930, thesystem memory 1925, and the permanent storage device 1935.

From these various memory units, the processing unit(s) 1910 retrievesinstructions to execute and data to process in order to execute theprocesses of the invention. The processing unit(s) may be a singleprocessor or a multi-core processor in different embodiments.

The read-only-memory (ROM) 1930 stores static data and instructions thatare needed by the processing unit(s) 1910 and other modules of theelectronic system. The permanent storage device 1935, on the other hand,is a read-and-write memory device. This device is a non-volatile memoryunit that stores instructions and data even when the electronic system1900 is off. Some embodiments of the invention use a mass-storage device(such as a magnetic or optical disk and its corresponding disk drive) asthe permanent storage device 1935.

Other embodiments use a removable storage device (such as a floppy disk,flash memory device, etc., and its corresponding drive) as the permanentstorage device. Like the permanent storage device 1935, the systemmemory 1925 is a read-and-write memory device. However, unlike storagedevice 1935, the system memory 1925 is a volatile read-and-write memory,such a random access memory. The system memory 1925 stores some of theinstructions and data that the processor needs at runtime. In someembodiments, the invention's processes are stored in the system memory1925, the permanent storage device 1935, and/or the read-only memory1930. From these various memory units, the processing unit(s) 1910retrieves instructions to execute and data to process in order toexecute the processes of some embodiments.

The bus 1905 also connects to the input and output devices 1940 and1945. The input devices 1940 enable the user to communicate informationand select commands to the electronic system. The input devices 1940include alphanumeric keyboards and pointing devices (also called “cursorcontrol devices”), cameras (e.g., webcams), microphones or similardevices for receiving voice commands, etc. The output devices 1945display images generated by the electronic system or otherwise outputdata. The output devices 1945 include printers and display devices, suchas cathode ray tubes (CRT) or liquid crystal displays (LCD), as well asspeakers or similar audio output devices. Some embodiments includedevices such as a touchscreen that function as both input and outputdevices.

Finally, as shown in FIG. 19, bus 1905 also couples electronic system1900 to a network 1965 through a network adapter (not shown). In thismanner, the computer can be a part of a network of computers (such as alocal area network (“LAN”), a wide area network (“WAN”), or an Intranet,or a network of networks, such as the Internet. Any or all components ofelectronic system 1900 may be used in conjunction with the invention.

Some embodiments include electronic components, such as microprocessors,storage and memory that store computer program instructions in amachine-readable or computer-readable medium (alternatively referred toas computer-readable storage media, machine-readable media, ormachine-readable storage media). Some examples of such computer-readablemedia include RAM, ROM, read-only compact discs (CD-ROM), recordablecompact discs (CD-R), rewritable compact discs (CD-RW), read-onlydigital versatile discs (e.g., DVD-ROM, dual-layer DVD-ROM), a varietyof recordable/rewritable DVDs (e.g., DVD-RAM, DVD-RW, DVD+RW, etc.),flash memory (e.g., SD cards, mini-SD cards, micro-SD cards, etc.),magnetic and/or solid state hard drives, read-only and recordableBlu-Ray® discs, ultra density optical discs, any other optical ormagnetic media, and floppy disks. The computer-readable media may storea computer program that is executable by at least one processing unitand includes sets of instructions for performing various operations.Examples of computer programs or computer code include machine code,such as is produced by a compiler, and files including higher-level codethat are executed by a computer, an electronic component, or amicroprocessor using an interpreter.

While the above discussion primarily refers to microprocessor ormulti-core processors that execute software, some embodiments areperformed by one or more integrated circuits, such as applicationspecific integrated circuits (ASICs) or field programmable gate arrays(FPGAs). In some embodiments, such integrated circuits executeinstructions that are stored on the circuit itself. In addition, someembodiments execute software stored in programmable logic devices(PLDs), ROM, or RAM devices.

As used in this specification and any claims of this application, theterms “computer”, “server”, “processor”, and “memory” all refer toelectronic or other technological devices. These terms exclude people orgroups of people. For the purposes of the specification, the termsdisplay or displaying means displaying on an electronic device. As usedin this specification and any claims of this application, the terms“computer readable medium,” “computer readable media,” and “machinereadable medium” are entirely restricted to tangible, physical objectsthat store information in a form that is readable by a computer. Theseterms exclude any wireless signals, wired download signals, and anyother ephemeral signals.

This specification refers throughout to computational and networkenvironments that include virtual machines (VMs). However, virtualmachines are merely one example of data compute nodes (DCNs) or datacompute end nodes, also referred to as addressable nodes. DCNs mayinclude non-virtualized physical hosts, virtual machines, containersthat run on top of a host operating system without the need for ahypervisor or separate operating system, and hypervisor kernel networkinterface modules.

VMs, in some embodiments, operate with their own guest operating systemson a host using resources of the host virtualized by virtualizationsoftware (e.g., a hypervisor, virtual machine monitor, etc.). The tenant(i.e., the owner of the VM) can choose which applications to operate ontop of the guest operating system. Some containers, on the other hand,are constructs that run on top of a host operating system without theneed for a hypervisor or separate guest operating system. In someembodiments, the host operating system uses name spaces to isolate thecontainers from each other and therefore provides operating-system levelsegregation of the different groups of applications that operate withindifferent containers. This segregation is akin to the VM segregationthat is offered in hypervisor-virtualized environments that virtualizesystem hardware, and thus can be viewed as a form of virtualization thatisolates different groups of applications that operate in differentcontainers. Such containers are more lightweight than VMs.

Hypervisor kernel network interface modules, in some embodiments, is anon-VM DCN that includes a network stack with a hypervisor kernelnetwork interface and receive/transmit threads. One example of ahypervisor kernel network interface module is the vmknic module that ispart of the ESXi™ hypervisor of VMware, Inc.

It should be understood that while the specification refers to VMs, theexamples given could be any type of DCNs, including physical hosts, VMs,non-VM containers, and hypervisor kernel network interface modules. Infact, the example networks could include combinations of different typesof DCNs in some embodiments.

Additionally, the term “packet” is used throughout this application torefer to a collection of bits in a particular format sent across anetwork. It should be understood that the term “packet” may be usedherein to refer to various formatted collections of bits that may besent across a network. A few examples of such formatted collections ofbits are Ethernet frames, TCP segments, UDP datagrams, IP packets, etc.

While the invention has been described with reference to numerousspecific details, one of ordinary skill in the art will recognize thatthe invention can be embodied in other specific forms without departingfrom the spirit of the invention. In addition, a number of the figures(including FIGS. 6 and 8) conceptually illustrate processes. Thespecific operations of these processes may not be performed in the exactorder shown and described. The specific operations may not be performedin one continuous series of operations, and different specificoperations may be performed in different embodiments. Furthermore, theprocess could be implemented using several sub-processes, or as part ofa larger macro process. Thus, one of ordinary skill in the art wouldunderstand that the invention is not to be limited by the foregoingillustrative details, but rather is to be defined by the appendedclaims.

1-20. (canceled)
 21. A method for using a managed hardware forwardingelement (MHFE) to perform packet forwarding operations for a logicalnetwork, the method comprising: receiving at the MHFE data that definesa logical router and a plurality of logical switches of the logicalnetwork that connects a plurality of end machines operating on aplurality of host computers to a plurality of physical machines that areconnected to the MHFE; using the received data to configure a set offorwarding tables of the MHFE in order to define the logical router andthe plurality of logical switches on the WIFE; and using the set offorwarding tables at the MHFE to perform packet forwarding operationsfor the logical network, wherein the logical router spans the MHFE andforwarding elements on the host computers that implement the logicalrouter, while each logical switch spans the MHFE and the forwardingelements on host computers that implement the logical switch.
 22. Themethod of claim 21, wherein the plurality of logical switches arelogically connected through the logical router.
 23. The method of claim21, wherein a set of the forwarding elements on a set of host computersare software forwarding elements executing on the set of host computers.24. The method of claim 21, wherein the received data includes dataregarding the logical ports of the logical switches and logical routers.25. The method of claim 24, wherein the received data comprises: foreach logical port of the logical router, a network address and a datalink address; for each logical port of each logical switch, linking datacomprising a corresponding network address for each data link address ofeach port that is associated with a logical switch, including thelogical ports of the logical router.
 26. The method of claim 25, whereinthe MHFE identifies the logical network packets that are destined forthe logical router by identifying a destination data link address in adata link header of a received packet of the logical network, anddetermining that the identified data link address is a data link addressof a logical port of a logical router by identifying a correspondingnetwork address of the identified destination data link address of thereceived packet, and matching the retrieved network address against anetwork address of the logical port.
 27. The method of claim 24, whereinthe set of forwarding tables of the MHFE comprises first and secondtables, wherein using the received data to configure the set offorwarding tables comprises: for each logical port of each logicalswitch, storing in the first forwarding table linking data foridentifying the logical router when the logical port is connected to alogical port of the logical router; and for the logical router, storingin the second forwarding table a set routes for the logical router touse to perform forwarding operations.
 28. The method of claim 27,wherein using the set of forwarding tables comprises using the first andsecond forwarding tables to perform packet forwarding operations at theMHFE.
 29. The method of claim 27, wherein the first table further storesa tunnel endpoint address for a forwarding element that executes on ahost computer to implement a logical switch that is associated with aport of a logical network element in order to establish a tunnel betweenthe MHFE and the host computer that executes the forwarding element. 30.The method of claim 27, wherein the first and second tables are linkedin order to enable the MHFE to identify logical network packets that aredestined for the logical router, wherein the MHFE performs logicalforwarding operations on the identified logical network packets byreplacing source and destination data link addresses in a data linkheader of the packet in order to route the packet to a next hop or adestination of the packet.
 31. A non-transitory machine readable mediumstoring a program for using a managed hardware forwarding element (MHFE)to perform packet forwarding operations for a logical network, theprogram comprising sets of instructions for: receiving at the MHFE datathat defines a logical router and a plurality of logical switches of thelogical network that connects a plurality of end machines operating on aplurality of host computers to a plurality of physical machines that areconnected to the MHFE; using the received data to configure a set offorwarding tables of the MHFE in order to define the logical router andthe plurality of logical switches on the MHFE; and using the set offorwarding tables at the MHFE to perform packet forwarding operationsfor the logical network, wherein the logical router spans the MHFE andforwarding elements on the host computers that implement the logicalrouter, while each logical switch spans the MHFE and the forwardingelements on host computers that implement the logical switch.
 32. Thenon-transitory machine readable medium of claim 31, wherein theplurality of logical switches are logically connected through thelogical router.
 33. The non-transitory machine readable medium of claim31, wherein a set of the forwarding elements on a set of host computersare software forwarding elements executing on the set of host computers.34. A method for configuring a managed hardware forwarding element(MHFE) to perform packet forwarding operations for a logical network,the method comprising: receiving data for the logical network thatdefines a logical router and a set of logical switches for logicallyconnecting a plurality of end machines operating on a plurality of hostmachines to a plurality of physical machines that are connected to theMHFE; defining a plurality of routing components for the logical routerbased on the received logical network data, each routing componentcomprising a separate set of logical ports; and configuring a forwardingtable on the MHFE by populating the forwarding table with tunnelendpoint data for each logical port of each routing component of thelogical router that is associated with a logical port of a logicalswitch.
 35. The method of claim 34, wherein each logical switch in theset of logical switches is implemented by the MHFE and by a set ofmanaged forwarding elements (MFEs), each MFE operating on a host machineon which a subset of the plurality of end machines reside.
 36. Themethod of claim 34, wherein the tunnel endpoint data populated for eachlogical port of the remaining routing components in the plurality ofrouting components indicate a tunnel endpoint network address for an MFEthat implements a logical switch in order to establish a tunnel from theMHFE to the MFE for exchanging network data.
 37. The method of claim 36,wherein the logical switch comprises logical switch one of ports ofwhich is associated with a logical port of the routing component forwhich the tunnel is established.
 38. The method of claim 35, wherein theparticular routing component comprises a distributed router that is alsoimplemented by both the MHFE and MFEs, wherein every other routingcomponent in the plurality of routing components comprises a servicerouter that is neither implemented by the MHFE nor by any of the MFEs.39. The method of claim 38, wherein the logical router further connectsthe logical network to one or more external physical networks, whereineach service router is implemented on a gateway machine that connectsthe logical network to one or more external physical networks.
 40. Themethod of claim 38 further comprising, based on the definition of thelogical router, defining a transit logical switch for logically handlingtraffic between the distributed router and the service routers, whereinthe MHFE, gateway machines, and MFEs further implement the transitlogical switch.